Light-emitting device having fluorescent and phosphorescent materials

ABSTRACT

It is an object to provide a flexible light-emitting device with long lifetime in a simple way and to provide an inexpensive electronic device with long lifetime using the flexible light-emitting device. A flexible light-emitting device is provided, which includes a substrate having flexibility and a light-transmitting property with respect to visible light; a first adhesive layer over the substrate; an insulating film containing nitrogen and silicon over the first adhesive layer; a light-emitting element including a first electrode, a second electrode facing the first electrode, and an EL layer between the first electrode and the second electrode; a second adhesive layer over the second electrode; and a metal substrate over the second adhesive layer, wherein the thickness of the metal substrate is 10 μm to 200 μm inclusive. Further, an electronic device using the flexible light-emitting device is provided.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a light-emitting device and a methodfor manufacturing the light-emitting device. Further, the presentinvention relates to an electronic device on which the light-emittingdevice is mounted.

2. Description of the Related Art

In recent years, technological development has been remarkably made inthe field of displays. In particular, the needs of the market havestimulated tremendous progress in the technology directed to increase inresolution of displays and thinning of displays.

In the next phase of this field, focus is placed on commercialization ofa flexible display having a curved display area, and a variety ofproposals have been made on manufacturing the flexible display (forexample, Patent Document 1). A light-emitting device using a flexiblesubstrate can be highly lightweight compared to the case of using aglass substrate or the like.

However, in commercialization of such a flexible display, the biggestproblem is its short lifetime.

The lifetime of the flexible display is short because, for a substratewhich should support a light-emitting element and protect the elementfrom moisture, oxygen, or the like of the surroundings, a glasssubstrate that is not flexible cannot be used, and instead, a plasticsubstrate which has flexibility but high permeability and low heatresistance has to be used. Since the heat resistance of the plasticsubstrate is low, a protective film with high quality which needs ahigh-temperature process cannot be formed, and moisture entering throughthe plastic substrate has a great influence on the lifetime of thelight-emitting element, furthermore, the light-emitting device. InNon-Patent Document 1, for example, an example in which a light-emittingelement is formed over a substrate including polyethersulfone (PES) as abase and is sealed with an aluminum film to form a flexiblelight-emitting device is introduced; however, its lifetime is about 230hours and the light-emitting device is miles away fromcommercialization. In Non-Patent Documents 2 and 3, an example of aflexible light-emitting device in which a light-emitting element isformed over a stainless steel substrate is introduced. In this flexiblelight-emitting device, moisture is prevented from entering through thestainless steel substrate; however, moisture cannot be preventedeffectively from entering from the light-emitting element side.Therefore, as an attempt to improve the lifetime of the flexiblelight-emitting device, it is manufactured over the stainless steelsubstrate, and a sealing film obtained by repeatedly stacking pluralkinds of materials is employed for the light-emitting element side.

Although a metal thin film such as an aluminum film or a stainless steelsubstrate has both flexibility and low permeability, it does nottransmit visible light therethrough with a normal thickness. Thus, inthe light-emitting device, a metal thin film or a stainless steelsubstrate is used for only one of a pair of substrates which sandwich alight-emitting element.

REFERENCE Patent Document

-   [Patent Document 1]-   Japanese Published Patent Application No. 2003-204049

Non Patent Document

-   [Non Patent Document 1]-   Gi Heon Kim et al., IDW'03, 2003, pp. 387-390-   [Non Patent Document 2]-   Dong Un Jin et al., SID 06 DIGEST, 2006, pp. 1855-1857-   [Non Patent Document 3]-   Anna Chwang et al., SID 06 DIGEST, 2006, pp. 1858-1861

SUMMARY OF THE INVENTION

In Non Patent Document 1, the lifetime of the light-emitting device isshort, and the reason is probably as follows: although moisture isprevented from entering from an upper portion which is sealed with analuminum film, moisture cannot be prevented from entering through thePES substrate. In addition, the heat resistance of the light-emittingelement used for such a light-emitting device is low, and thus, it isdifficult to form a protective film with high quality after forming thelight-emitting element.

In Non Patent Documents 2 and 3, it seems that the lifetime of thelight-emitting device is the same as that of a light-emitting deviceinterposed between glass substrates; however, this lifetime is achievedsince a sealing film obtained by repeatedly stacking plural kinds ofmaterials as described above is used, and the productivity is low. Thelow productivity results in a high price, and such a light-emittingdevice is not realistic.

As described above, in a flexible light-emitting device, since a plasticsubstrate which has lower heat resistance than a conventionally-usedglass substrate has been used, a dense protective film which is formedat high temperature cannot be used and the lifetime of a light-emittingelement or a light-emitting device has been short. Furthermore, asealing film which is used for complementing the plastic substrate ispoor in productivity.

In addition, since a plastic substrate is used for a flexiblelight-emitting device, a flexible light-emitting device is more oftenelectrically charged than a light-emitting device using a glasssubstrate or the like. Therefore, in a flexible light-emitting device, amalfunction due to some sort of cause could possibly occur, for example,a malfunction due to static electricity may occur when staticelectricity is discharged from human bodies and electric charge isaccumulated in a flexible light-emitting device.

In view of the above, it is an object of one embodiment of the presentinvention to provide a flexible light-emitting device with long lifetimein a simple way. In addition, it is another object to provide anelectronic device using the flexible light-emitting device. Further, itis still another object to provide a flexible light-emitting devicewhich is resistant to static electricity.

The above object can be achieved with a flexible light-emitting devicewhich is manufactured in the following manner. That is, a protectivefilm is formed over a substrate with high heat resistance such as aglass substrate at an appropriate temperature so as to have sufficientlylow permeability, and necessary components such as a thin filmtransistor (hereinafter also referred to a TFT) and an electrode of alight-emitting element or a TFT and a light-emitting element are formedover the protective film. After that, the necessary components aretransferred to a plastic substrate together with the protective film,and finally, a metal substrate is adhered thereto using an adhesive.

That is, one embodiment of the invention disclosed in this specificationis a flexible light-emitting device which includes: a substrate havingflexibility and a light-transmitting property with respect to visiblelight; a first adhesive layer provided over the substrate; an insulatingfilm containing nitrogen and silicon provided over the first adhesivelayer; a light-emitting element including a first electrode providedover the insulating film, a second electrode facing the first electrode,and an EL layer provided between the first electrode and the secondelectrode; a second adhesive layer provided over the second electrode;and a metal substrate provided over the second adhesive layer, whereinthe thickness of the metal substrate is 10 μm to 200 μm inclusive.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device which includes: asubstrate having flexibility and a light-transmitting property withrespect to visible light; a first adhesive layer provided over thesubstrate; an insulating film containing nitrogen and silicon providedover the first adhesive layer; a thin film transistor formation layer(hereinafter referred to a TFT formation layer) provided over theinsulating film; a light-emitting element including a first electrodewhich is electrically connected to a part of a TFT provided in the TFTformation layer, a second electrode facing the first electrode, and anEL layer provided between the first electrode and the second electrode;a second adhesive layer provided over the second electrode; and a metalsubstrate provided over the second adhesive layer, wherein the thicknessof the metal substrate is 10 μm to 200 μm inclusive.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein an active layer of the TFT formed in the TFTformation layer is formed using crystalline silicon.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure which further includes: a pixel portion including a pluralityof light-emitting elements; and a driver circuit portion providedoutside the pixel portion, wherein the driver circuit portion includes aTFT formed in the TFT formation layer.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein a film sealing layer is formed between the secondelectrode of the light-emitting element and the second adhesive layer.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein the metal substrate is formed using a material suchas stainless steel, aluminum, copper, nickel, or an aluminum alloy.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein the first adhesive layer is formed using at least oneof an epoxy resin, an acrylic resin, a silicone resin, and a phenolresin.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein the second adhesive layer is formed using at leastone of an epoxy resin, an acrylic resin, a silicone resin, and a phenolresin.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein a resin layer is further provided over the metalsubstrate.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein the resin layer includes at least one of thermalcurable resins such as an epoxy resin, an acrylic resin, a siliconeresin, a phenol resin, and a polyester resin, or at least one ofthermoplastic resins such as polypropylene, polyethylene, polycarbonate,polystyrene, polyamide, polyetherketone, a fluorine resin, andpolyethylenenaphthalate.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein at least one of the substrate having flexibility anda light-transmitting property with respect to visible light, the firstadhesive layer, the second adhesive layer, and the resin layer includesa fibrous body.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein a film having low permeability is formed between thesubstrate having flexibility and a light-transmitting property withrespect to visible light and the first adhesive layer.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein the film having low permeability is a film containingsilicon and nitrogen or a film containing aluminum and nitrogen.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein a coat film is provided over a surface of thesubstrate having flexibility and a light-transmitting property withrespect to visible light, which is opposite to a surface facing themetal substrate.

In addition, another embodiment of the invention disclosed in thisspecification is a flexible light-emitting device having the abovestructure, wherein the coat film has a light-transmitting property withrespect to visible light and high hardness. Further, when a conductivefilm having a light-transmitting property with respect to visible lightis used for the coat film, the flexible light-emitting device can beprotected from static electricity.

In addition, another embodiment of the invention disclosed in thisspecification is an electronic device using the flexible light-emittingdevice having the above structure for a display portion.

In addition, another embodiment of the invention disclosed in thisspecification is a method for manufacturing a flexible light-emittingdevice, which includes the steps of: forming a separation layer over aformation substrate; forming an insulating film containing nitrogen andsilicon over the separation layer; forming a first electrode over theinsulating film; forming a partition wall so as to cover an end portionof the first electrode; adhering a temporary supporting substrate to thefirst electrode and the partition wall; separating the insulating film,the first electrode, the partition wall, and the temporary supportingsubstrate from the formation substrate by using the separation layer;adhering a substrate having flexibility and a light-transmittingproperty with respect to visible light to a surface of the insulatingfilm, which is exposed by the separation, using a first adhesive layer;removing the temporary supporting substrate to expose a surface of thefirst electrode; forming an EL layer containing an organic compound soas to cover the exposed first electrode; forming a second electrode soas to cover the EL layer; and adhering a metal substrate having athickness of 10 μm to 200 μm inclusive to a surface of the secondelectrode using a second adhesive layer.

In addition, another embodiment of the invention disclosed in thisspecification is a method for manufacturing a flexible light-emittingdevice, which includes the steps of: forming a separation layer over aformation substrate; forming an insulating film containing nitrogen andsilicon over the separation layer; forming a TFT formation layerincluding a plurality of TFTs over the insulating film; forming a firstelectrode which is electrically connected to a part of a TFT provided inthe TFT formation layer, over the TFT formation layer; forming apartition wall so as to cover an end portion of the first electrode;adhering a temporary supporting substrate to the first electrode and thepartition wall; separating the insulating film, the TFT formation layer,the first electrode, the partition wall, and the temporary supportingsubstrate from the formation substrate by using the separation layer;adhering a substrate having flexibility and a light-transmittingproperty with respect to visible light to a surface of the insulatingfilm, which is exposed by the separation, using a first adhesive layer;removing the temporary supporting substrate to expose a surface of thefirst electrode; forming an EL layer containing an organic compound soas to cover the exposed first electrode; forming a second electrode soas to cover the EL layer; and adhering a metal substrate having athickness of 10 μm to 200 μm inclusive to a surface of the secondelectrode using a second adhesive layer.

In addition, another embodiment of the invention disclosed in thisspecification is the above method for manufacturing a flexiblelight-emitting device, wherein, after the metal substrate is adhered, aresin layer is formed over the metal substrate.

In addition, another embodiment of the invention disclosed in thisspecification is the above method for manufacturing a flexiblelight-emitting device, wherein a film sealing layer is formed betweenthe second electrode and the second adhesive layer.

In addition, another embodiment of the invention disclosed in thisspecification is the above method for manufacturing a flexiblelight-emitting device, wherein the insulating film is formed by a plasmaCVD method at a temperature of 250° C. to 400° C. inclusive.

A light-emitting device according to one embodiment of the presentinvention is a flexible light-emitting device which has long lifetimeand can be manufactured in a simple way even though it is flexible. Inaddition, one embodiment of the present invention can provide a methodcapable of manufacturing a flexible light-emitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C each illustrate a light-emitting device according to anembodiment.

FIGS. 2A to 2D each illustrate a light-emitting device according to anembodiment.

FIGS. 3A to 3E illustrate a manufacturing process of a light-emittingdevice according to an embodiment.

FIGS. 4A to 4C each illustrate a light-emitting device according to anembodiment.

FIGS. 5A to 5E each illustrate an electronic device according to anembodiment.

FIGS. 6A and 6B each illustrate a structure of a light-emitting elementaccording to an embodiment.

FIGS. 7A to 7C illustrate a light-emitting device according to anexample.

FIGS. 8A and 8B illustrate a light-emitting device according to anexample.

FIG. 9 illustrates a light-emitting device according to an example.

FIG. 10 illustrates a light-emitting device according to an example.

FIGS. 11A and 11B each illustrate a light-emitting device according toan embodiment.

FIGS. 12A to 12C illustrate a light-emitting device according to anembodiment.

FIG. 13 illustrates a protective film according to an example.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. However, the present inventioncan be carried out in many different modes, and it is easily understoodby those skilled in the art that modes and details thereof can bemodified in various ways without departing from the spirit and the scopeof the present invention. Therefore, the present invention should not beinterpreted as being limited to the description of the embodiments.

Embodiment 1

A light-emitting device in this embodiment is manufactured in thefollowing manner: after a layer to be separated which includes aprotective film (the layer to be separated may also include a TFT, afirst electrode of a light-emitting element, a light-emitting element,and/or the like) is formed over a formation substrate having high heatresistance such as a glass substrate or a ceramic substrate with aseparation layer interposed therebetween, the formation substrate andthe layer to be separated are separated at the separation layer, and thelayer to be separated which is separated is adhered to a plasticsubstrate using an adhesive. Therefore, the protective film which hassufficiently low permeability is provided over the high-permeabilityplastic substrate, and the light-emitting device in this embodiment hasa first adhesive layer between the plastic substrate and the protectivefilm. The plastic substrate in this specification is a substrate havingflexibility and a light-transmitting property with respect to visiblelight. There is no particular limitation on the plastic substrate aslong as it has flexibility and a light-transmitting property withrespect to visible light, but it is preferable to use a polyester resinsuch as polyethylene terephthalate (PET) or polyethylene naphthalate(PEN), a polyacrylonitrile resin, a polyimide resin, a polymethylmethacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES)resin, a polyamide resin, a cycloolefin resin, a polystyrene resin, apolyamide imide resin, a polyvinylchloride resin, or the like. Inaddition, the first adhesive layer is formed using a material having alight-transmitting property with respect to visible light. For example,any of a variety of types of curable adhesive, e.g., a light curableadhesive such as a UV curable adhesive, a reactive curable adhesive, athermal curable adhesive, and an anaerobic adhesive can be used. As suchan adhesive, an epoxy resin, an acrylic resin, a silicone resin, aphenol resin, or the like is used. The protective film is formed using amaterial having low permeability and a light-transmitting property withrespect to visible light. For example, an insulating film containingnitrogen and silicon, such as a silicon nitride film, a silicon nitrideoxide film, or a silicon oxynitride film is preferably used.

A metal substrate is used as a substrate which faces the plasticsubstrate with the light-emitting element interposed therebetween. Themetal substrate employed has a thickness of 10 μm to 200 μm inclusive soas to be flexible. Note that a metal substrate with a thickness of 20 μmto 100 μm inclusive is preferable because of its high flexibility. Amaterial of the metal substrate is not limited to a particular material,but it is preferable to use aluminum, copper, nickel, an alloy such asan aluminum alloy or stainless steel, or the like. Since the metalsubstrate does not have a light-transmitting property with respect tovisible light with a thickness in the above range although it hassufficiently low permeability and high flexibility, the light-emittingdevice in this embodiment is a so-called bottom emission light-emittingdevice in which light emission is extracted through the plasticsubstrate provided with a TFT layer. Note that the metal substrate isadhered to the light-emitting element with an adhesive layer interposedtherebetween in a manner similar to the plastic substrate, and thus, asecond adhesive layer is provided between a second electrode of thelight-emitting element or a film sealing layer and the metal substrate.As a material of the second adhesive layer, a reactive curable adhesive,a thermal curable adhesive, an anaerobic adhesive, or the like can beused. Such an adhesive is made of an epoxy resin, an acrylic resin, asilicone resin, a phenol resin, or the like.

In the flexible light-emitting device in this embodiment with such astructure, over the high-permeability plastic substrate, the protectivefilm with sufficiently low permeability which is formed at a temperatureof greater than or equal to the upper temperature limit of the plasticsubstrate is provided, whereby the influence of moisture which entersthrough the plastic substrate can be effectively reduced. In addition,since the metal substrate having high flexibility and low permeabilityis used as a sealing substrate which faces the plastic substrate withthe light-emitting element interposed therebetween, the influence ofmoisture which enters through the sealing substrate can also beeffectively suppressed. In this manner, on both sides of thelight-emitting element, it is possible to effectively reduce moisturewhich enters without stacking a plurality of films; therefore, theflexible light-emitting device in this embodiment is a flexiblelight-emitting device with long lifetime which can be easilymanufactured.

A TFT, a light-emitting element, and the like may be formed in additionto the protective film in the layer to be separated which is formed overthe formation substrate. As a TFT, a TFT which can be manufacturedwithout a high-temperature process, such as a TFT using amorphoussilicon or a TFT using an oxide semiconductor can be used. In addition,it is also possible to manufacture a TFT using a crystallinesemiconductor layer which requires a certain degree of heating or laserprocessing, such as crystalline silicon, by forming a TFT over theformation substrate having high heat resistance. Accordingly, theflexible light-emitting device in this embodiment can be an activematrix flexible light-emitting device including a TFT which uses acrystalline semiconductor. In addition, since a TFT using a crystallinesemiconductor can be used, a driver circuit portion or a CPU can beformed over the same substrate as that for a pixel portion. Thus, aflexible light-emitting device which has great advantages in cost andmanufacturing process can be manufactured, differing from the case wherea driver circuit portion or a CPU is provided separately.

FIGS. 1A to 1C each illustrate a light-emitting device of thisembodiment.

FIG. 1A illustrates an example of a flexible light-emitting deviceprovided with a driver circuit portion and a pixel TFT. Over a plasticsubstrate 110, a first adhesive layer 111 is provided. With the firstadhesive layer 111, a protective film 112 and the plastic substrate 110are adhered to each other. Over the protective film 112, a baseinsulating film 113, a pixel TFT 114, a TFT 115 for the driver circuitportion, a first electrode 117 of a light-emitting element which iselectrically connected to the pixel TFT 114, and a partition wall 118which covers an end portion of the first electrode 117, which arepartially illustrated in FIG. 1A, are provided. A light-emitting element127 includes the first electrode 117 which is exposed from the partitionwall 118, an EL layer 119 which is formed so as to cover at least theexposed first electrode 117 and contains an organic compound, and asecond electrode 120 which is provided to cover the EL layer 119. Ametal substrate 122 is adhered to the second electrode 120 with a secondadhesive layer 121. Note that the driver circuit portion is notnecessarily provided, and a CPU portion may be provided. In addition, inFIG. 1A, a layer 116 to be separated includes at least the protectivefilm 112, the base insulating film 113, the pixel TFT 114, the TFT 115for the driver circuit portion, a first interlayer insulating film 128,a second interlayer insulating film 129, the first electrode 117, andthe partition wall 118, but this is just an example which can be easilymanufactured and the components included in the layer 116 to beseparated are not limited thereto.

FIG. 1B illustrates an example of a passive matrix flexiblelight-emitting device. As in FIG. 1A, a first adhesive layer 111 isprovided over a plastic substrate 110. With the first adhesive layer111, a layer 116 to be separated and the plastic substrate 110 areadhered to each other. The layer 116 to be separated includes aprotective film 112, a first electrode 117 of a light-emitting element,and a partition wall 118, which are partially illustrated in FIG. 1B. Alight-emitting element 127 includes the first electrode 117 which isexposed from the partition wall 118, an EL layer 119 which is formed soas to cover at least the exposed first electrode 117 and contains anorganic compound, and a second electrode 120 which is provided in astripe shape to cover the EL layer 119. A metal substrate 122 is adheredto the second electrode 120 with a second adhesive layer 121. In FIG.1B, the layer 116 to be separated includes at least the protective film112, the first electrode 117, and the partition wall 118, but this isjust an example which can be easily manufactured and the componentsincluded in the layer 116 to be separated are not limited thereto.Although FIG. 1B illustrates an example of the passive matrixlight-emitting device in which the partition wall 118 has a taperedshape, a passive matrix light-emitting device in which the partitionwall 118 has an inversely tapered shape may also be used. In such acase, the EL layer 119 and the second electrode 120 can be separatelyprovided due to the inversely tapered partition wall 118, so thatpatterning using a mask is not necessary in formation of the EL layer119 and the second electrode 120.

Note that as illustrated in FIG. 1C, a resin layer 123 may be furtherprovided over the metal substrate 122 to protect the metal substrate122. Alternatively, a coat film 124 may be provided on the surface ofthe plastic substrate 110, which is opposite to the surface in contactwith the first adhesive layer 111, so as to protect the surface of theplastic substrate from pressure or scratches. Further alternatively, asubstrate which is provided with a protective film 125 with lowpermeability in advance may be used as the plastic substrate 110, or astructure in which moisture that enters the light-emitting device isfurther suppressed by providing a film sealing layer 126 over the secondelectrode 120 may be employed. The resin layer 123 can be formed usingone or more of thermal curable resin materials such as an epoxy resin,an acrylic resin, a silicone resin, a phenol resin, and a polyesterresin, or one or more of thermoplastic resin materials such aspolypropylene, polyethylene, polycarbonate, polystyrene, polyamide,polyetherketone, a fluorine resin, and polyethylenenaphthalate. Further,the coat film 124 can be formed with various types of materials such asan organic film, an inorganic film, or a stack film including theorganic film and the inorganic film, and means a hard coat film (such asa silicon nitride film) which can protect the surface of the softplastic substrate 110 from scratches or the like, or a film (such as anaramid resin film) which can disperse pressure. The coat film 124 ispreferably a film having a light-transmitting property with respect tovisible light and high hardness. As the protective film 125 which isformed over the plastic substrate in advance or the film sealing layer126, a film containing nitrogen and silicon, such as a silicon nitridefilm or a silicon nitride oxide film can be used, for example.

In the flexible light-emitting device in FIG. 1C, moisture that entersthrough the surfaces of the substrates is effectively suppressed by theprotective film 112 and the metal substrate 122; thus, the protectivefilm 125 or the film sealing layer 126 is effective because permeabilityis further supplementarily reduced. Note that as for the above fourcomponents, that is, the resin layer 123, the coat film 124, theprotective film 125, and the film sealing layer 126, any one of them,two or more of them, or all of them may be employed. Although thestructure of FIG. 1C is manufactured based on the structure of FIG. 1A,these components may also be combined with the structure of FIG. 1B.

In FIGS. 1A to 1C, only one light-emitting element 127 is illustrated;however, in the case where the flexible light-emitting device in thisembodiment is used for displaying an image, a pixel portion including aplurality of the light-emitting elements 127 is formed. When afull-color image is displayed, it is necessary to obtain light of atleast three colors, i.e., red, green, and blue. As a method forobtaining light of at least three colors, there are a method in which anecessary portion of each EL layer 119 is formed using an appropriatematerial in accordance with the color of light emission, a method inwhich each color is obtained by forming all light-emitting elements foremitting light of white and transmitting the light through a colorfilter layer, a method in which each color is obtained by forming alllight-emitting elements for emitting light of blue or other colors witha shorter wavelength than blue and transmitting the light through acolor conversion layer, and the like.

FIGS. 2A to 2D each illustrate how a color filter layer or a colorconversion layer is placed. In FIGS. 2A to 2D, reference numeral 300denotes a color filter layer (or a color conversion layer), andreference numeral 301 denotes a barrier film. The barrier film 301 isplaced so as to protect a light-emitting element or a TFT from influenceof a gas generated from the color filter layer (or the color conversionlayer) 300, but is not necessarily provided. The color filter layer (orthe color conversion layer) 300 is provided for a light-emitting element127 of each color. And the adjacent color filter layers may beoverlapped at a portion other than an open region (a portion where thefirst electrode, the EL layer, and the second electrode are directlyoverlapped) of the light-emitting element 127. The color filter layer300 and the barrier film 301 may be formed only in the pixel portion ormay be formed also in the driver circuit portion.

In FIG. 2A, after an electrode 307 of a TFT is formed, the color filterlayer 300 is formed over an interlayer insulating film 304 of the TFT,and a planarization film 306 is formed using an organic insulating filmso as to planarize a step by the color filter layer. After that, acontact hole is formed in the planarization film 306, an electrode 305which connects the first electrode 117 of the light-emitting element andthe electrode 307 of the TFT is formed, and the first electrode 117 ofthe light-emitting element is provided. The barrier film 301 may beprovided over the planarization film 306.

In addition, as illustrated in FIG. 2B, the color filter layer 300 maybe provided below the interlayer insulating film 304. In FIG. 2B, afterthe barrier film 301 is formed, the color filter layer 300 is formedover the barrier film 301. After that, the interlayer insulating film304 and the electrode 305 of the TFT are formed, and the first electrode117 of the light-emitting element is provided.

Although FIGS. 2A to 2D each illustrate only a color filter layer (or acolor conversion layer) of a single color, color filter layers (or colorconversion layers) of red, green, and blue are formed at appropriatepositions with appropriate shapes in a light-emitting device. Anyarrangement can be adopted for the arrangement pattern of the colorfilter layers (or the color conversion layers), and stripe arrangement,diagonal mosaic arrangement, triangle mosaic arrangement, and the likemay be used. In addition, in the case of using a white light-emittingelement and a color filter layer, RGBW four pixel arrangement may beused. The RGBW four pixel arrangement is pixel arrangement which has apixel provided with a color filter layer transmitting light of red, apixel provided with a color filter layer transmitting light of blue, apixel provided with a color filter layer transmitting light of green,and a pixel not provided with a color filter layer; this arrangement iseffective in reducing power consumption and the like. Light emitted fromthe white light-emitting element includes, for example, light of red,light of green, and light of blue, preferably, those according to theNational Television Standard Committee (NTSC).

The color filter layer can be formed by using a known material. In thecase of using a photosensitive resin as the color filter layer, thecolor filter layer may be patterned by exposing the color filter layeritself to light and then developing it, but it is preferred to performpatterning by dry etching since a minute pattern is necessary.

FIG. 2C illustrates an example of a structure in which a color filtersubstrate 302 provided with the color filter layer 300 is provided. Inthe case where the surface of the color filter substrate 302, which isnot provided with the color filter layer 300, is attached to the plasticsubstrate 110 with an adhesive layer 308 which is formed with the samematerial as the first adhesive layer 111, the color filter substrate 302may be provided with a coat film 303 for protecting the color filterlayer 300 from scratches and the like. The coat film 303 is formed witha material having a light-transmitting property with respect to visiblelight, and the same material as that for the coat film 124 can be used.In addition, although not illustrated, the surface of the color filtersubstrate 302, which is provided with the color filter layer 300, may beattached to the plastic substrate 110. Note that the color filtersubstrate 302 is a substrate obtained by forming the color filter layer300 on any of various types of substrates having flexibility and alight-transmitting property with respect to visible light, for example,a substrate formed using a material similar to that for the plasticsubstrate 110.

FIG. 2D illustrates an example of a structure in which the color filtersubstrate 302 obtained by providing, in advance, the color filter layer300 for the plastic substrate 110 is directly attached to the layer 116to be separated which has the first electrode. The color filtersubstrate 302 including the plastic substrate 110 provided with thecolor filter layer 300 is directly attached to the layer 116 to beseparated which includes the first electrode, whereby the number ofcomponents can be reduced and the manufacturing cost can be reduced. Thecolor filter layer (or the color conversion layer) is provided, asbriefly described above. In addition to the above, a black matrix may beprovided between light-emitting elements, or other known structures maybe employed.

Next, as an example, a method for manufacturing a flexiblelight-emitting device in this embodiment including a TFT will bedescribed with reference to FIGS. 3A to 3E and FIGS. 1A to 1C.

First, the layer 116 to be separated including the TFT, the firstelectrode 117, and the like is formed over a formation substrate 200having an insulating surface, with a separation layer 201 interposedtherebetween (FIG. 3A).

As the formation substrate 200, a glass substrate, a quartz substrate, asapphire substrate, a ceramic substrate, a metal substrate provided withan insulating layer on the surface, or the like, which is a substratehaving heat resistance that is high enough to form a high-qualityprotective film can be used.

Since a substrate with low flexibility which can be used for manufacturenormal displays is used for the formation substrate, a pixel TFT forhigh-resolution display can be provided.

The separation layer 201 is formed by a sputtering method, a plasma CVDmethod, a coating method, a printing method, or the like to be a singlelayer or a stacked layer using an element such as tungsten (W),molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium (Nb), nickel(Ni), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium(Rh), palladium (Pd), osmium (Os), iridium (Ir), or silicon (Si); analloy material containing the element as its main component; or acompound material containing the element as its main component. Thecrystalline structure of a layer containing silicon may be any one of anamorphous state, a microcrystalline state, and a polycrystalline state.Note that a coating method includes a spin-coating method, a dropletdischarge method, a dispensing method, a nozzle-printing method, and aslot die coating method in its category here.

When the separation layer 201 has a single layer structure, it ispreferable to form a tungsten layer, a molybdenum layer, or a layercontaining a mixture of tungsten and molybdenum. Alternatively, a layercontaining an oxide or an oxynitride of tungsten, a layer containing anoxide or an oxynitride of molybdenum, or a layer containing an oxide oran oxynitride of a mixture of tungsten and molybdenum is formed. Notethat the mixture of tungsten and molybdenum corresponds to an alloy oftungsten and molybdenum, for example.

In the case where the separation layer 201 has a stacked layerstructure, a first layer is preferably formed using a tungsten layer, amolybdenum layer, or a layer containing a mixture of tungsten andmolybdenum, and a second layer is preferably formed using an oxide, anitride, an oxynitride, or a nitride oxide of tungsten, molybdenum, or amixture of tungsten and molybdenum.

In the case where the separation layer 201 has a stacked layer structureof a layer containing tungsten and a layer containing an oxide oftungsten, the layer containing tungsten may be formed first and aninsulating layer formed of an oxide may be formed over the layercontaining tungsten so that the layer containing an oxide of tungstencan be formed at an interface between the tungsten layer and theinsulating layer. This also applies to the case of forming a layercontaining a nitride, an oxynitride, or a nitride oxide of tungsten. Forexample, after a layer containing tungsten is formed, a silicon nitridelayer, a silicon oxynitride layer, or a silicon nitride oxide layer maybe formed thereover. Further, the surface of the layer containingtungsten may be subjected to thermal oxidation treatment, oxygen plasmatreatment, or treatment using a strong oxidizing solution such as ozonewater to form the layer containing an oxide of tungsten. Furthermore,plasma treatment or heat treatment may be performed in an atmosphere ofoxygen, nitrogen, dinitrogen monoxide, an elementary substance ofdinitrogen monoxide, or a mixed gas of any of these gases and anothergas.

The layer 116 to be separated is formed over the separation layer 201.In order to form the layer 116 to be separated, first, the protectivefilm 112 is formed over the separation layer 201. The protective film112 can be a film which is dense and has very low permeability byforming an insulating film containing nitrogen and silicon such as asilicon nitride film, a silicon oxynitride film, or a silicon nitrideoxide film by plasma CVD at a temperature in the range of 250° C. to400° C. while setting other conditions to be known conditions.

Then, the base insulating film 113 is formed in order to stabilize thecharacteristics of the TFT which is to be formed later. The baseinsulating film 113 can be formed as a single layer or a stacked layerby using an inorganic insulating film of silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, or the like. When theprotective film 112 also serves as an insulating film which is a base,the base insulating film 113 is not necessarily formed.

A semiconductor layer included in the transistor can be formed using anyof the following materials: an amorphous semiconductor (hereinafter alsoreferred to as “AS”) manufactured by a vapor-phase growth method using asemiconductor source gas typified by silane or germane or a sputteringmethod; a polycrystalline semiconductor formed by crystallizing theamorphous semiconductor with the use of light energy or thermal energy;a microcrystalline (also referred to as semi-amorphous or microcrystal)semiconductor (hereinafter also referred to as “SAS”); a semiconductorcontaining an organic material as its main component; and the like. Thesemiconductor layer can be formed by a sputtering method, an LPCVDmethod, a plasma CVD method, or the like.

The microcrystalline semiconductor layer belongs to an intermediatemetastable state between an amorphous semiconductor and a single crystalsemiconductor when Gibbs free energy is considered. That is, themicrocrystalline semiconductor layer is a semiconductor layer having athird state which is stable in terms of free energy and has a shortrange order and lattice distortion. Columnar-like or needle-likecrystals grow in a normal direction with respect to a substrate surface.

The Raman spectrum of microcrystalline silicon, which is a typicalexample of a microcrystalline semiconductor, is shifted to a wave numberlower than 520 cm⁻¹, which represents a peak of the Raman spectrum ofsingle crystal silicon. That is, the peak of the Raman spectrum of themicrocrystalline silicon exists between 520 cm⁻¹ which represents singlecrystal silicon and 480 cm⁻¹ which represents amorphous silicon. Themicrocrystalline silicon contains hydrogen or halogen of at least 1 at.% to terminate a dangling bond. Moreover, microcrystalline silicon ismade to contain a rare gas element such as helium, argon, krypton, orneon to further enhance its lattice distortion, whereby stability isincreased and a favorable microcrystalline semiconductor layer can beobtained.

This microcrystalline semiconductor layer can be formed by ahigh-frequency plasma CVD method with a frequency of several tens of MHzto several hundreds of MHz or with a microwave plasma CVD method with afrequency of greater than or equal to 1 GHz. For example, themicrocrystalline semiconductor layer can be formed with a dilution ofsilicon hydride such as SiH₄, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, or SiF₄with hydrogen. Further, in addition to silicon hydride and hydrogen, oneor plural kinds of rare gas elements selected from helium, argon,krypton, or neon are used for a dilution, so that the microcrystallinesemiconductor layer can be formed. In that case, the flow ratio ofhydrogen to silicon hydride is set to be 5:1 to 200:1, preferably, 50:1to 150:1, more preferably, 100:1.

As an example of an amorphous semiconductor, hydrogenated amorphoussilicon can be given, and as an example of a crystalline semiconductor,polysilicon or the like can be given. Examples of polysilicon(polycrystalline silicon) include so-called high-temperature polysiliconthat contains polysilicon which is formed at a process temperature ofgreater than or equal to 800° C. as its main component, so-calledlow-temperature polysilicon that contains polysilicon which is formed ata process temperature of less than or equal to 600° C. as its maincomponent, polysilicon obtained by crystallizing amorphous silicon byusing an element that promotes crystallization or the like, and thelike. It is needless to say that as mentioned above, a microcrystallinesemiconductor or a semiconductor containing a crystal phase in a part ofa semiconductor layer can be used.

As a material of the semiconductor layer, as well as an element such assilicon (Si) or germanium (Ge), a compound semiconductor such as GaAs,InP, SiC, ZnSe, GaN, or SiGe can be used. Alternatively, an oxidesemiconductor such as zinc oxide (ZnO), tin oxide (SnO₂), magnesium zincoxide, gallium oxide, or indium oxide, an oxide semiconductor includingtwo or more of the above oxide semiconductors, or the like can be used.For example, an oxide semiconductor including zinc oxide, indium oxide,and gallium oxide can also be used. In the case of using zinc oxide forthe semiconductor layer, the gate insulating film may be formed of Y₂O₃,Al₂O₃, or TiO₂, a stacked layer thereof, or the like, and the gateelectrode layer, the source electrode layer, and the drain electrodelayer may be formed of indium tin oxide (ITO), Au, Ti, or the like. Inaddition, In, Ga, or the like can be added to ZnO. Note that atransparent transistor using an oxide semiconductor film which transmitsvisible light as a semiconductor layer can also be used as a transistorin a pixel portion. When such a transparent transistor is formed so asto overlap with a light-emitting element, an area ratio of alight-emitting element in a pixel, that is, a so-called aperture ratiocan be increased, and a flexible display device with high luminance andhigh resolution can be formed. Further, when a gate electrode, a sourceelectrode, and a drain electrode of a transparent transistor are formedusing a conductive film which transmits visible light, an aperture ratiocan be further increased.

In the case of using a crystalline semiconductor layer for thesemiconductor layer, the crystalline semiconductor layer may be formedby any of various methods (such as a laser crystallization method, athermal crystallization method, and a thermal crystallization methodusing an element promoting crystallization, such as nickel). Also, amicrocrystalline semiconductor which is an SAS can be crystallized bybeing irradiated with laser light to increase its crystallinity. Whenthe element that promotes crystallization is not introduced, prior toirradiating an amorphous silicon film with laser light, the amorphoussilicon film is heated at 500° C. for one hour under a nitrogenatmosphere to release hydrogen contained in the amorphous silicon filmsuch that the concentration of hydrogen becomes less than or equal to1×10²⁰ atoms/cm³. This is because the amorphous silicon film isdestroyed when the amorphous silicon film containing a high amount ofhydrogen is irradiated with laser light.

A method for introducing a metal element into an amorphous semiconductorlayer is not limited to a particular method as long as it is a methodcapable of providing the metal element on a surface or inside of theamorphous semiconductor layer. For example, a sputtering method, a CVDmethod, a plasma processing method (including a plasma CVD method), anadsorption method, or a method for applying a solution of metal salt,can be used. In the above mentioned methods, the method using a solutionis simple and has an advantage that the concentration of a metal elementcan easily be adjusted. In addition, at this time, in order to improvethe wettability of the surface of the amorphous semiconductor layer tospread an aqueous solution on the entire surface of the amorphoussemiconductor layer, an oxide film is preferably formed by UV lightirradiation in an oxygen atmosphere, a thermal oxidation method,treatment using ozone water containing hydroxy radical or a hydrogenperoxide solution, or the like.

In addition, in a crystallization step in which the amorphoussemiconductor layer is crystallized to form a crystalline semiconductorlayer, the crystallization may be performed by adding an element whichpromotes crystallization (also referred to as a catalyst element or ametal element) to the amorphous semiconductor layer and performing heattreatment (at 550° C. to 750° C. for 3 minutes to 24 hours). As theelement which promotes (accelerates) the crystallization, one or more ofiron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh),palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), copper (Cu),and gold (Au) can be used.

In order to remove or reduce the element which promotes crystallizationfrom the crystalline semiconductor layer, a semiconductor layercontaining an impurity element is formed in contact with the crystallinesemiconductor layer and is made to function as a gettering sink. As theimpurity element, an impurity element imparting n-type conductivity, animpurity element imparting p-type conductivity, a rare gas element, orthe like can be used. For example, one or more of phosphorus (P),nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi), boron (B),helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can beused. The semiconductor layer containing a rare gas element is formedover the crystalline semiconductor layer containing an element whichpromotes crystallization, and heat treatment (at 550° C. to 750° C. for3 minutes to 24 hours) is performed. The element which promotescrystallization in the crystalline semiconductor layer moves into thesemiconductor layer containing a rare gas element, and the element whichpromotes crystallization in the crystalline semiconductor layer isremoved or reduced. Then, the semiconductor layer containing a rare gaselement, which serves as a gettering sink, is removed.

The amorphous semiconductor layer may be crystallized by usingcombination of heat treatment and laser light irradiation. The heattreatment or the laser light irradiation may be carried out severaltimes, separately.

Alternatively, the crystalline semiconductor layer may be directlyformed over the base insulating film over the formation substrate by aplasma method.

Alternatively, the crystalline semiconductor layer may be selectivelyformed over the base insulating film over the formation substrate by aplasma method.

As the semiconductor layer containing an organic material as its maincomponent, a semiconductor layer containing, as its main component, asubstance which contains a certain amount of carbon or an allotrope ofcarbon (excluding diamond), which is combined with another element, canbe used. Specifically, pentacene, tetracene, a thiophen oligomerderivative, a phenylene derivative, a phthalocyanine compound, apolyacetylene derivative, a polythiophene derivative, a cyanine dye, andthe like can be given.

The gate insulating film and the gate electrode may be formed with aknown structure and a known method. For example, the gate insulatingfilm may be formed with a known structure such as a single layerstructure of silicon oxide or a stacked layer structure includingsilicon oxide and silicon nitride, and the gate electrode may be formedusing any of Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe,Ti, Si, Ge, Zr, and Ba; or an alloy material or a compound materialcontaining any of the elements as its main component by a CVD method, asputtering method, a droplet discharge method, or the like. In addition,a semiconductor layer typified by a polycrystalline silicon film dopedwith an impurity element such as phosphorus or an AgPdCu alloy may beused. Further, either a single layer structure or a stacked layerstructure may be employed.

Note that although FIGS. 1A to 1C each illustrate an example of a topgate transistor, a bottom gate transistor or a transistor with otherknown structures may also be used.

Next, an interlayer insulating film is formed. The interlayer insulatingfilm can be formed using an inorganic insulating material or an organicinsulating material to have a single layer structure or a stacked layerstructure. As the organic insulating material, for example, acrylic,polyimide, polyamide, polyimide amide, benzocyclobutene, or the like canbe used. Although two interlayer insulating films 128 and 129 areillustrated in FIGS. 1A and 1C, this is just an example, and thestructure of the interlayer insulating film is not limited thereto.

The interlayer insulating film which is formed is patterned and etched,and a contact hole which reaches the semiconductor layer of thetransistor is formed in the interlayer insulating film, the gateinsulating film, and the like. Then, a conductive metal film isdeposited by a sputtering method or a vacuum evaporation method andetched to form an electrode and a wiring of the transistor. A drainelectrode of the pixel transistor is formed so as to partially overlapwith a first electrode which is a pixel electrode, whereby the drainelectrode of the pixel transistor and the first electrode areelectrically connected to each other.

Then, the first electrode 117 is formed using a conductive film having alight-transmitting property with respect to visible light. When thefirst electrode 117 is an anode, indium oxide (In₂O₃), an alloy ofindium oxide and tin oxide (In₂O₃—SnO₂:ITO), or the like can be used asa material of the conductive film having a light-transmitting propertywith respect to visible light, and the first electrode 117 can be formedby a sputtering method, a vacuum evaporation method, or the like.

Alternatively, an alloy of indium oxide and zinc oxide (In₂O₃—ZnO) maybe used. In addition, zinc oxide (ZnO) is also an appropriate material,and moreover, zinc oxide to which gallium (Ga) is added (ZnO:Ga) toincrease conductivity and a light-transmitting property with respect tovisible light, or the like can be used. When the first electrode 117 isa cathode, an extremely thin film of a material with a low work functionsuch as aluminum can be used. Alternatively, a stacked layer structurewhich has a thin layer of such a substance and the above-mentionedconductive film having a light-transmitting property with respect tovisible light can be employed.

Then, an insulating film is formed using an organic insulating materialor an inorganic insulating material so as to cover the interlayerinsulating film and the first electrode 117. The insulating film isprocessed such that the surface of the first electrode 117 is exposedand the insulating film covers an end portion of the first electrode117, whereby the partition wall 118 is formed.

Through the above process, the layer 116 to be separated can be formed.

Next, the layer 116 to be separated and a temporary supporting substrate202 are adhered to each other using an adhesive 203 for separation,which is followed by separation of the layer 116 to be separated fromthe formation substrate 200 at the separation layer 201. By thisprocess, the layer 116 to be separated is placed on the temporarysupporting substrate 202 side (FIG. 3B).

As the temporary supporting substrate 202, a glass substrate, a quartzsubstrate, a sapphire substrate, a ceramic substrate, a metal substrate,and the like can be used. Further, a plastic substrate which has heatresistance high enough to resist a temperature of the manufacturingprocess of this embodiment, or a flexible substrate such as a film maybe used.

As the adhesive 203 for separation which is used here, an adhesive whichis soluble in water or a solvent, an adhesive which is capable of beingplasticized upon irradiation of UV light, and the like are used so thatthe temporary supporting substrate 202 and the layer 116 to be separatedcan be chemically or physically separated when necessary.

Any of various methods can be used as appropriate as the process fortransferring the layer to be separated to the temporary supportingsubstrate. When, as the separation layer, a film including a metal oxidefilm is formed on the side in contact with the layer to be separated,the metal oxide film is embrittled by being crystallized, and thus thelayer to be separated can be separated from the formation substrate.When an amorphous silicon film containing hydrogen is formed as theseparation layer between the formation substrate having high heatresistance and the layer to be separated, by removing the amorphoussilicon film by laser light irradiation or etching, the layer to beseparated can be separated from the formation substrate. In addition,after a film including a metal oxide film is formed as the separationlayer on the side in contact with the layer to be separated, the metaloxide film is embrittled by being crystallized, and a part of theseparation layer is removed by etching using a solution or a halogenfluoride gas such as NF₃, BrF₃, or ClF₃, the separation can be performedat the embrittled metal oxide film. Furthermore, a method may be used inwhich a film containing nitrogen, oxygen, hydrogen, or the like (forexample, an amorphous silicon film containing hydrogen, an alloy filmcontaining hydrogen, an alloy film containing oxygen, or the like) isused as the separation layer, and the separation layer is irradiatedwith laser light to release the nitrogen, oxygen, or hydrogen containedin the separation layer as a gas, thereby promoting separation betweenthe layer to be separated and the formation substrate.

Furthermore, a method in which the formation substrate over which thelayer to be separated is formed is removed mechanically or by etchingusing a solution or a halogen fluoride gas such as NF₃, BrF₃, or ClF₃,or the like may be used. In this case, the separation layer is notnecessarily provided.

When a plurality of the above-described separation methods are combined,the transfer process can be conducted easily. For example, separationcan be performed with physical force (by a machine or the like) afterperforming laser light irradiation, etching on the separation layer witha gas, a solution, or the like, or mechanical removal with a sharpknife, scalpel, or the like so that the separation layer and the layerto be separated can be easily separated from each other.

Alternatively, separation of the layer to be separated from theformation substrate may be carried out after a liquid is made topenetrate an interface between the separation layer and the layer to beseparated. Further alternatively, the separation may be performed whilepouring a liquid such as water during the separation.

As another separation method, when the separation layer 201 is formedusing tungsten, the separation may be performed while the separationlayer 201 is etched with the use of a mixed solution of ammonia waterand a hydrogen peroxide solution.

Next, the layer 116 to be separated which is separated from theformation substrate 200 to expose the separation layer 201 or theprotective film 112 is adhered to the plastic substrate 110 using thefirst adhesive layer 111 which is formed of a different adhesive fromthe adhesive 203 for separation (FIG. 3C).

As a material of the first adhesive layer 111, various curableadhesives, e.g., a light curable adhesive such as a UV curable adhesive,a reactive curable adhesive, a thermal curable adhesive, and ananaerobic adhesive can be used.

As the plastic substrate 110, any of a variety of substrates havingflexibility and a light-transmitting property with respect to visiblelight can be used, and a film of an organic resin or the like ispreferably used. As the organic resin, for example, a polyester resinsuch as polyethylene terephthalate (PET) or polyethylene naphthalate(PEN), an acrylic resin, a polyacrylonitrile resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, apolystyrene resin, a polyamide imide resin, a polyvinylchloride resin,or the like can be used.

Over the plastic substrate 110, the protective film 125 having lowpermeability, such as a film containing nitrogen and silicon, e.g.,silicon nitride or silicon oxynitride, a film containing nitrogen andaluminum such as aluminum nitride, or an aluminum oxide film may beformed in advance.

After that, the temporary supporting substrate 202 is removed bydissolving or plasticizing the adhesive 203 for separation. After thetemporary supporting substrate 202 is removed, the adhesive 203 forseparation is removed using water, a solvent, or the like to allow thefirst electrode 117 of the light-emitting element to be exposed (FIG.3D).

Through the above-mentioned process, the layer 116 to be separated,which includes components such as the TFT and the first electrode 117 ofthe light-emitting element, can be manufactured over the plasticsubstrate 110.

After the first electrode 117 is exposed, the EL layer 119 is formed.There is no particular limitation on a stacked layer structure of the ELlayer 119. A layer containing a substance having a highelectron-transporting property, a layer containing a substance having ahigh hole-transporting property, a layer containing a substance having ahigh electron-injecting property, a layer containing a substance havinga high hole-injecting property, a layer containing a bipolar substance(a substrate having a high electron-transporting property and a highhole-transporting property), and the like are appropriately combined.For example, an appropriate combination of any of a hole-injectinglayer, a hole-transporting layer, a light-emitting layer, anelectron-transporting layer, an electron-injecting layer, and the likecan be formed. In this embodiment, a structure is explained in which theEL layer includes a hole-injecting layer, a hole-transporting layer, alight-emitting layer, and an electron-transporting layer. Specificmaterials to form each of the layers are given below.

The hole-injecting layer is a layer that is provided in contact with ananode and contains a substance with a high hole-injecting property.Specifically, molybdenum oxide, vanadium oxide, ruthenium oxide,tungsten oxide, manganese oxide, or the like can be used. Alternatively,the hole-injecting layer can also be formed using any of the followingmaterials: a phthalocyanine compound such as phthalocyanine (H₂PC) orcopper phthalocyanine (CuPc); an aromatic amine compound such as4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (DPAB) or4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(DNTPD); a high-molecular compound such aspolyethylenedioxythiophene/polystyrenesulfonic acid (PEDOT/PSS); and thelike.

Alternatively, as the hole-injecting layer, a composite materialcontaining a substance with a high hole-transporting property and anacceptor substance can be used. Note that, by using the compositematerial containing the substance with a high hole-transporting propertyand the acceptor substance, a material used to form an electrode can beselected regardless of its work function. In other words, besides amaterial with a high work function, a material with a low work functioncan also be used as the first electrode 117. As the acceptor substance,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F₄-TCNQ),chloranil, and the like can be given. In addition, a transition metaloxide is given. In addition, oxides of metals that belong to Group 4 toGroup 8 of the periodic table can be given. Specifically, vanadiumoxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferablebecause of their high electron-accepting properties. Among these metaloxides, molybdenum oxide is preferable since it can be easily treateddue to its stability in the air and low hygroscopic property.

As the substance having a high hole-transporting property used for thecomposite material, any of various compounds such as an aromatic aminecompound, a carbazole derivative, aromatic hydrocarbon, and ahigh-molecular compound (such as oligomer, dendrimer, or polymer) can beused. Note that the organic compound used for the composite material ispreferably an organic compound having a high hole-transporting property.Specifically, a substance having a hole mobility of greater than orequal to 10⁻⁶ cm²/Vs is preferably used. However, other substances thanthese substances may also be used as long as a hole-transportingproperty thereof is higher than an electron-transporting propertythereof. The organic compound that can be used for the compositematerial is specifically shown below.

Examples of the aromatic amine compounds includeN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (DTDPPA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (DPAB),4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(DNTPD), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(DPA3B), and the like.

Examples of the carbazole derivatives which can be used for thecomposite material include3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(PCzPCA2),3-[N-(1-naphtyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(PCzPCN1), and the like.

In addition, examples of the carbazole derivatives which can be used forthe composite material include 4,4′-di(N-carbazolyl)biphenyl (CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (CzPA),1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and thelike.

Examples of the aromatic hydrocarbon which can be used for the compositematerial include 2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA),2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (t-BuDBA),9,10-di(2-naphthyl)anthracene (DNA), 9,10-diphenylanthracene (DPAnth),2-tert-butylanthracene (t-BuAnth),9,10-bis(4-methyl-1-naphthyl)anthracene (DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, andthe like. As well as these compounds, pentacene, coronene, or the likecan be used. As described above, use of an aromatic hydrocarbon whichhas a hole mobility of greater than or equal to 1×10⁻⁶ cm²/Vs and has 14to 42 carbon atoms is more preferable.

The aromatic hydrocarbon that can be used for the composite material mayhave a vinyl skeleton. As an aromatic hydrocarbon having a vinyl group,for example, 4,4′-bis(2,2-diphenylvinyl)biphenyl (DPVBi),9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (DPVPA), and the likeare given.

High-molecular compounds such as poly(N-vinylcarbazole) (PVK),poly(4-vinyltriphenylamine) (PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N-phenylamino}phenyl)methacrylamide](PTPDMA),poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine](Poly-TPD), andthe like can also be used.

The hole-transporting layer is a layer that contains a substance with ahigh hole-transporting property. Examples of the substance having a highhole-transporting property include aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (BSPB),and the like. The substances described here are mainly substances havinga hole mobility of greater than or equal to 10⁻⁶ cm²/Vs. However, asubstance other than the above-described substances may also be used aslong as a hole-transporting property thereof is higher than anelectron-transporting property thereof. Note that the layer containingthe substance with a high hole-transporting property is not limited to asingle layer, and two or more layers containing the aforementionedsubstances may be stacked.

Further, a high-molecular compound such as poly(N-vinylcarbazole) (PVK)or poly(4-vinyltriphenylamine) (PVTPA) can also be used for thehole-transporting layer.

The light-emitting layer is a layer containing a light-emittingsubstance. The light-emitting layer may be a so-called singlelight-emitting layer containing a light-emitting substance as its maincomponent or a so-called host-guest type light-emitting layer in which alight-emitting substance is dispersed in a host material.

There is no particular limitation on the light-emitting substance thatis used, and known fluorescent materials or phosphorescent materials canbe used. As fluorescent materials, for example, in addition toN,N-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(YGA2S), 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(YGAPA), and the like, there are fluorescent materials with an emissionwavelength of greater than or equal to 450 nm, such as4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(PCBAPA),N,N′-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N,N-triphenyl-1,4-phenylenediamine](DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N,N-triphenyl-1,4-phenylenediamine(2DPAPPA),N,N′,N′,N″,N″,N′,N″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N-triphenyl-1,4-phenylenediamine(2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(2YGABPhA), N,N,9-triphenylanthracen-9-amine (DPhAPhA), coumarin 545T,N,N′-diphenylquinacridone (DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(DCM2), N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine(p-mPhTD),7,13-diphenyl-N,N,N′,N-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(BisDCJTM). As phosphorescent materials, for example, in addition tobis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate(FIr6) and the like, there are phosphorescent materials with an emissionwavelength in the range of 470 nm to 500 nm, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(Flrpic),bis[2-(3′,5′-bistrifluoromethylphenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(Ir(CF₃ppy)₂(pic)), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate(FIracac); phosphorescent materials with an emission wavelength ofgreater than or equal to 500 nm (materials which emit green light), suchas tris(2-phenylpyridinato)iridium(III) (Ir(ppy)₃),bis(2-phenylpyridinato)iridium(III)acetylacetonate (Ir(ppy)₂(acac)),tris(acetylacetonato)(monophenanthroline)terbium(III) (Tb(acac)₃(Phen)),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (Ir(bzq)₂(acac)),bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(Ir(dpo)₂(acac)),bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate(Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(Ir(bt)₂(acac)),bis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate(Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(Ir(tppr)₂(acac)),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinatoplatinum(II) (PtOEP),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(Eu(DBM)₃(Phen)), and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (Eu(TTA)₃(Phen)); and the like. Thelight-emitting substances can be selected from the above-mentionedmaterials or other known materials in consideration of the emissioncolor of each of the light-emitting elements.

When the host material is used, for example, the following can be given:metal complexes such as tris(8-quinolinolato)aluminum(III) (Alq),tris(4-methyl-8-quinolinolato)aluminum(III) (Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq),bis(8-quinolinolato)zinc(II) (Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (ZnBTZ); heterocycliccompounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ),2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBI),bathophenanthroline (BPhen), bathocuproine (BCP), and9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (CO11); andaromatic amine compounds such as NPB (or α-NPD), TPD, and BSPB. Inaddition, condensed polycyclic aromatic compounds such as anthracenederivatives, phenanthrene derivatives, pyrene derivatives, chrysenederivatives, and dibenzo[g,p]chrysene derivatives are given. Thefollowing is specifically given as the condensed polycyclic aromaticcompound: 9,10-diphenylanthracene (DPAnth);N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(CzA1PA); 4-(10-phenyl-9-anthryl)triphenylamine (DPhPA);4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (YGAPA);N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(PCAPA);N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(PCAPBA); N-9-diphenyl-N-(9,10-diphenyl-2-anthryl)-9H-carbazol-3-amine(2PCAPA); 6,12-dimethoxy-5,11-diphenylchrysene,N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetramine(DBC1); 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (CzPA);3,6-diphenyl-9-[4-(10-phenyl-9-antryl)phenyl]-9H-carbazole (DPCzPA),9,10-bis(3,5-diphenylphenyl)anthracene (DPPA),9,10-di(2-naphthyl)anthracene (DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA), 9,9′-bianthryl(BANT), 9,9′-(stilbene-3,3′-diyl)diphenanthrene (DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (TPB3), and the like. From thesesubstances or other known substances, the host material may be selectedso that the host material has a larger energy gap (or triplet excitationenergy if the light-emitting substance emits phosphorescence) than thelight-emitting substance dispersed in the light-emitting layer and has acarrier-transporting property required for each of the light-emittinglayers.

The electron-transporting layer is a layer that contains a substancewith a high electron-transporting property. For example, a layercontaining a metal complex having a quinoline skeleton or abenzoquinoline skeleton, such as tris(8-quinolinolato)aluminum (Alq),tris(4-methyl-8-quinolinolato)aluminum (Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (BeBq₂), orbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (BAlq) can beused. Alternatively, a metal complex having an oxazole-based orthiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (Zn(BTZ)₂) canbe used. Besides the metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ),bathophenanthroline (BPhen), bathocuproine (BCP), or the like can alsobe used. The substances described here are mainly those having anelectron mobility of greater than or equal to 10⁻⁶ cm²/Vs. Note that asubstance other than the above substances may also be used as theelectron-transporting layer as long as an electron-transporting propertythereof is higher than a hole-transporting property thereof.

Further, the electron-transporting layer may be formed as not only asingle layer but also as a stacked layer in which two or more layersformed using the above mentioned substances are stacked.

Further, a layer for controlling transport of electrons may be providedbetween the electron-transporting layer and the light-emitting layer.The layer for controlling transport of electrons is a layer in which asmall amount of a substance having a high electron-trapping property isadded to a layer containing the above-mentioned substances having a highelectron-transporting property. The layer for controlling transport ofelectrons controls transport of electrons, which enables adjustment ofcarrier balance. Such a structure is very effective in suppressing aproblem (such as shortening of element lifetime) caused by a phenomenonthat an electron passes through the light-emitting layer.

Further, an electron-injecting layer may be provided so as to be incontact with the electrode functioning as a cathode. As theelectron-injecting layer, an alkali metal, an alkaline earth metal, or acompound thereof, such as lithium fluoride (LiF), cesium fluoride (CsF),calcium fluoride (CaF₂), or the like can be employed. For example, alayer which contains both a substance having an electron-transportingproperty and an alkali metal, an alkaline earth metal, or a compoundthereof, e.g., a layer of Alq containing magnesium (Mg), can be used.Note that electrons can be efficiently injected from the secondelectrode 120 by using, as the electron-injecting layer, a layercontaining a substance having an electron-transporting property to whichan alkali metal or an alkaline earth metal is added.

The second electrode 120 is formed over the EL layer 119. When thesecond electrode 120 is used as a cathode, a metal, an alloy, anelectrically conductive compound, a mixture thereof, or the like havinga low work function (specifically, a work function of less than or equalto 3.8 eV), can be used as a substance for the second electrode 120. Asa specific example of such a cathode material, an element belonging toGroup 1 or Group 2 of the periodic table, i.e., an alkali metal such aslithium (Li) or cesium (Cs), an alkaline earth metal such as magnesium(Mg), calcium (Ca), or strontium (Sr), an alloy containing any of thesemetals (such as MgAg or AlLi), a rare earth metal such as europium (Eu)or ytterbium (Yb), an alloy containing such a rare earth metal, or thelike can be used. However, when the electron-injecting layer is providedbetween the cathode and the electron-transporting layer, any of avariety of conductive materials such as Al, Ag, ITO, indium oxide-tinoxide containing silicon or silicon oxide, and the like can be usedregardless of its work function as the cathode. Films of theseconductive materials can be formed by a sputtering method, an ink-jetmethod, a spin coating method, or the like.

It is preferable that, when the second electrode 120 is used as ananode, the second electrode 120 be formed using a metal, an alloy, aconductive compound, a mixture thereof, or the like having a high workfunction (specifically greater than or equal to 4.0 eV). In specific, anexample thereof is indium oxide-tin oxide (ITO: indium tin oxide),indium oxide-tin oxide containing silicon or silicon oxide, indiumoxide-zinc oxide (IZO: indium zinc oxide), indium oxide containingtungsten oxide and zinc oxide (IWZO), or the like. Such conductive metaloxide films are usually formed by a sputtering method, but may also beformed by using a sol-gel method or the like. For example, indiumoxide-zinc oxide (IZO) can be formed by a sputtering method using atarget in which 1 wt % to 20 wt % of zinc oxide is added to indiumoxide. Indium oxide containing tungsten oxide and zinc oxide (IWZO) canbe formed by a sputtering method using a target in which 0.5 wt % to 5wt % of tungsten oxide and 0.1 wt % to 1 wt % of zinc oxide are added toindium oxide. In addition, gold (Au), platinum (Pt), nickel (Ni),tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co),copper (Cu), palladium (Pd), a nitride of a metal material (such astitanium nitride), or the like can be given. By forming theabove-mentioned composite material so as to be in contact with theanode, a material for the electrode can be selected regardless of itswork function.

Note that a plurality of the above-mentioned EL layers may be formedbetween a first electrode 600 and a second electrode 601 as illustratedin FIG. 6A. In this case, a charge generation layer 803 is preferablyprovided between stacked EL layers 800 and 801. The charge generationlayer 803 can be formed by using the above-mentioned composite material.Further, the charge generation layer 803 may have a stacked layerstructure including a layer containing the composite material and alayer containing another material. In this case, as the layer containinganother material, a layer containing a substance with anelectron-donating property and a substance with a highelectron-transporting property, a layer of a conductive film having alight-transmitting property with respect to visible light, and the likecan be used. As for a light-emitting element having such a structure,problems such as energy transfer and quenching occur with difficulty,and a light-emitting element which has both high light emissionefficiency and long lifetime can be easily obtained due to expansion inthe choice of materials. Moreover, a light-emitting element whichprovides phosphorescence from one of the EL layers and fluorescence fromthe other of the EL layers can be readily obtained. Note that thisstructure can be combined with the above-mentioned structures of the ELlayer.

Next, the case where two or more EL layers are stacked between the firstelectrode and the second electrode will be described. As illustrated inFIG. 6B, in the case of a structure in which n (n is a natural number of2 or more) EL layers 1003 are stacked, a charge generation layer 1004 isprovided between an m-th (m is a natural number, 1≤m≤n−1) EL layer andan (m+1)-th EL layer.

Note that the charge generation layer 1004 has a function of injectingholes to one EL layer 1003 which is formed in contact with the chargegeneration layer 1004 and a function of injecting electrons to the otherEL layer 1003 which is formed in contact with the charge generationlayer 1004, when voltage is applied to a first electrode 1001 and asecond electrode 1002.

The charge generation layer 1004 can be formed using, for example, acomposite material of an organic compound and a metal oxide. Inaddition, the charge generation layer 1004 can be formed with acombination of the composite material of an organic compound and a metaloxide with another material (such as an alkali metal, an alkaline metal,or a compound thereof). For example, a stacked layer structure includinga layer formed using the composite material of an organic compound and ametal oxide and a layer formed using another material (such as an alkalimetal, an alkaline metal, or a compound thereof) may be employed. Thecomposite material of an organic compound and a metal oxide includes,for example, an organic compound and a metal oxide such as V₂O₅, MoO₃,or WO₃. As the organic compound, various compounds such as an aromaticamine compound, a carbazole derivative, aromatic hydrocarbon, and ahigh-molecular compound (such as oligomer, dendrimer, or polymer) can beused. Note that an organic compound having a hole mobility of greaterthan or equal to 10⁻⁶ cm²/Vs is preferably used as a hole-transportingorganic compound. However, other substances may also be used as long asa hole-transporting property thereof is higher than anelectron-transporting property thereof. These materials used for thecharge generation layer 1004 are excellent in carrier-injecting propertyand carrier-transporting property, and thus, a light-emitting elementwhich can be driven with low current can be obtained.

In particular, the structure of FIG. 6A is preferable in the case ofobtaining white light emission. When the structure of FIG. 6A iscombined with any of the structures in FIGS. 2A to 2D, a full-colorflexible light-emitting device with long lifetime and high efficiencycan be manufactured.

As for the combination of a plurality of light-emitting layers, astructure for emitting white light by including light of red, light ofgreen, and light of blue may be used. For example, the structure mayinclude a first EL layer containing a blue fluorescent material as alight-emitting substance and a second EL layer containing red and greenphosphorescent materials as light-emitting substances. Also with astructure including light-emitting layers emitting light ofcomplementary colors, white light emission can be obtained. When lightemission from the first EL layer and light emission from the second ELlayer have complementary colors to each other in an element includingtwo EL layers stacked, the combination of colors are as follows: blueand yellow, blue-green and red, and the like. A substance which emitslight of blue, yellow, blue-green, or red light may be selected asappropriate from, for example, the light-emitting substances givenabove.

The following will describe an example of a structure in which whitelight emission can be obtained by including a plurality oflight-emitting layers (a first EL layer and a second EL layer) emittinglight of complementary colors.

For example, the first EL layer includes a first light-emitting layerwhich exhibits light emission with a spectrum whose peak is in thewavelength range of blue to blue-green, and a second light-emittinglayer which exhibits light emission with a spectrum whose peak is in thewavelength range of yellow to orange. The second EL layer includes athird light-emitting layer which exhibits light emission with a spectrumwhose peak is in the wavelength range of blue-green to green, and afourth light-emitting layer which exhibits light emission with aspectrum whose peak is in the wavelength range of orange to red.

In this case, light emission from the first EL layer is a combination oflight emission from both the first light-emitting layer and the secondlight-emitting layer and thus exhibits a light emission spectrum havingpeaks both in the wavelength range of blue to blue-green and in thewavelength range of yellow to orange. That is, the first EL layerexhibits light emission which has a 2-wavelength-type white color or a2-wavelength-type color that is similar to white.

In addition, light emission from the second EL layer is a combination oflight emission from both the third light-emitting layer and the fourthlight-emitting layer and thus exhibits a light emission spectrum havingpeaks both in the wavelength range of blue-green to green and in thewavelength range of orange to red. That is, the second EL layer exhibitslight emission which has a 2-wavelength-type white color or a2-wavelength-type color that is similar to white, which is differentfrom the first EL layer.

Accordingly, by combining the light-emission from the first EL layer andthe light emission from the second EL layer, white light emission whichcovers the wavelength range of blue to blue-green, the wavelength rangeof blue-green to green, the wavelength range of yellow to orange, andthe wavelength range of orange to red can be obtained.

Note that in the structure of the above-mentioned stacked element, byproviding the charge generation layer between the stacked EL layers, theelement can have long lifetime in a high-luminance region while keepingthe current density low. In addition, the voltage drop due to resistanceof the electrode material can be reduced, whereby uniform light emissionin a large area is possible.

When the components up to the second electrode 120 are formed, the metalsubstrate 122 is adhered to the second electrode 120 with the secondadhesive layer 121. The second adhesive layer 121 can be formed using amaterial similar to that of the first adhesive layer 111. A material forforming the metal substrate is not limited to a particular material, butit is preferable to use aluminum, copper, nickel, an alloy such as analuminum alloy or stainless steel, or the like (FIG. 3E). Before themetal substrate 122 is adhered with the second adhesive layer 121,preferably, baking or plasma treatment is performed in vacuum so thatwater attached to the surface of the metal substrate 122 is removed.

The metal substrate 122 can also be adhered with the use of a laminator.For example, there are a method in which a sheet-like adhesive isattached to the metal substrate using a laminator and the metalsubstrate with the sheet-like adhesive is further adhered to thelight-emitting element using a laminator, a method in which an adhesiveis printed on the metal substrate by screen printing or the like and themetal substrate with the adhesive is adhered to the light-emittingelement using a laminator, and the like. These processes are preferablyperformed under reduced pressure in order to reduce bubbles between thelight-emitting element and the metal substrate.

In the above manner, a light-emitting device according to one embodimentof the present invention as illustrated in FIGS. 1A to 1C can bemanufactured.

This embodiment describes a method in which a flexible light-emittingdevice having a TFT is formed by forming the components up to the firstelectrode 117 of the light-emitting element over the formation substrateand separating them, but the invention disclosed in this specificationis not limited thereto. After the components up to the light-emittingelement 127 are formed (that is, after the second electrode 120 of thelight-emitting element is formed), the components may be separated andtransferred. Alternatively, after only the protective film 112 may beformed over the formation substrate, and separated and transferred tothe plastic substrate 110, a TFT or a light-emitting element may bemanufactured. In the case where a TFT is not provided, thelight-emitting device can be manufactured in a similar manner bystarting the process from the formation of the first electrode 117 ofthe light-emitting element over the protective film 112.

Note that after the second electrode 120 of the light-emitting elementis formed, the film sealing layer 126 may be formed so as to furtherreduce permeability, as illustrated in FIG. 1C. In addition, the coatfilm 124 may be provided on the surface of the plastic substrate 110,which is opposite to the surface in contact with the first adhesivelayer 111, thereby preventing scratches on the screen or breaking due tothe pressure. Furthermore, the resin layer 123 may be provided over themetal substrate 122 to protect the metal substrate.

In addition, the plastic substrate 110, the first adhesive layer 111,the second adhesive layer 121, and the resin layer 123 may include afibrous body therein. The fibrous body is a high-strength fiber of anorganic compound or an inorganic compound. A high-strength fiber isspecifically a fiber with a high tensile modulus of elasticity or afiber with a high Young's modulus. As a typical example of ahigh-strength fiber, a polyvinyl alcohol based fiber, a polyester basedfiber, a polyamide based fiber, a polyethylene based fiber, an aramidbased fiber, a polyparaphenylene benzobisoxazole fiber, a glass fiber,or a carbon fiber can be given. As the glass fiber, a glass fiber usingE glass, S glass, D glass, Q glass, or the like can be given. Thesefibers may be used in a state of a woven fabric or a nonwoven fabric,and impregnated with an organic resin, and the organic resin is cured toobtain a structure body. This structure body may be used as the plasticsubstrate 110. When the structure body including the fibrous body andthe organic resin is used as the plastic substrate 110, reliabilityagainst bending or breaking due to local pressure can be increased,which is preferable.

In the case where the plastic substrate 110 or the first adhesive layer111 includes the above-mentioned fibrous body, in order to reduceprevention of light emitted from the light-emitting element to theoutside, the fibrous body is preferably a nanofiber with a diameter ofless than or equal to 100 nm. Further, refractive indexes of the fibrousbody and the organic resin or the adhesive preferably match with eachother.

In addition, the structure body obtained by the process in which thefibrous body is impregnated with the organic resin and the organic resinis cured can also be used to serve as both the first adhesive layer 111and the plastic substrate 110. At this time, as the organic resin forthe structure body, a reactive curable resin, a thermal curable resin, aUV curable resin, or the like which is better cured by additionaltreatment is preferably used.

Then, a flexible printed circuit (FPC) is attached to each electrode ofan input-output terminal portion with an anisotropic conductive member.An IC chip or the like may also be mounted if necessary.

Through the above process, a module type light-emitting device to whichthe FPC is connected is completed.

FIG. 4A is a top view and FIGS. 4B and 4C are cross-sectional views of amodule type light-emitting device (also referred to as an EL module).

FIG. 4A is a top view illustrating an EL module, and FIG. 4B is across-sectional view along line A-A′ of FIG. 4A. In FIG. 4A, aprotective film 501 is provided over a plastic substrate 110 with afirst adhesive layer 500 interposed therebetween. Over the protectivefilm 501, a pixel portion 502, a source side driver circuit 504, and agate side driver circuit 503 are formed.

Reference numeral 400 denotes a second adhesive layer and referencenumeral 401 denotes a metal substrate. The second adhesive layer 400 isformed over the pixel portion and the driver circuit portions, and themetal substrate 401 is adhered with the second adhesive layer 400.Further, the metal substrate 401 may be protected by providing a resinlayer thereover.

Reference numeral 508 denotes a wiring for transmitting signals input tothe source side driver circuit 504 and the gate side driver circuit 503,which receives video signals or clock signals from a flexible printedcircuit (FPC) 402 which is an external input terminal. Although only theFPC 402 is illustrated here, this FPC may be provided with a printedwiring board (PWB). The flexible light-emitting device disclosed in thisspecification means not only the light-emitting device itself but also acondition in which the FPC or the PWB is attached to the light-emittingdevice.

Next, a cross-sectional structure will be described with reference toFIG. 4B. The protective film 501 is provided on and in contact with thefirst adhesive layer 500, the pixel portion 502 and the gate side drivercircuit 503 are formed over the protective film 501, and the pixelportion 502 includes a plurality of pixels each including a currentcontrol TFT 511 and a pixel electrode 512 electrically connected to adrain of the current control TFT 511. Further, the gate side drivercircuit 503 is formed using a CMOS circuit that combines an n-channelTFT 513 and a p-channel TFT 514.

FIG. 4C illustrates an example of a cross-sectional structure which isdifferent from FIG. 4B. In the example of FIG. 4C, a partition wall 118is formed using an inorganic material such as silicon nitride, siliconoxynitride, silicon nitride oxide, or silicon oxide. The peripheral endportions of the second adhesive layer 400 and the metal substrate 401are placed closer to the center of the flexible light-emitting devicethan the peripheral end portion of the partition wall 118. That is, theareas of the second adhesive layer 400 and the metal substrate 401 aresmaller than the area of the partition wall 118, and the second adhesivelayer 400 and the metal substrate 401 are placed over the partition wall118 so as not to extend beyond the partition wall 118. Then, alow-melting point metal 520 is formed so as to cover the side surface ofthe second adhesive layer 400. With the low-melting point metal 520,moisture can be blocked highly effectively at the end portion on theside surface of the second adhesive layer 400, and thus, the lifetime ofthe flexible light-emitting device can be further improved. Thelow-melting point metal 520 is not limited to a particular metal, but ametal material which can be fused at approximately 45° C. to 300° C. ispreferably used. When the fusion temperature is about 300° C., thetemperature rises locally in the peripheral portion of the pixel portionand over the partition wall, and the low-melting point metal can befused without damaging the light-emitting element or the plasticsubstrate. As such a material, a metal material containing tin, silver,copper, indium, or the like can be given. In addition, bismuth or thelike may be further contained therein.

FIGS. 11A and 11B illustrate other structures which can effectivelyprevent moisture from entering from the peripheral end portion of thelight-emitting device. The metal substrate 401 of the light-emittingdevice illustrated in FIG. 11A is larger than the second adhesive layer400, a light-emitting element 518, the layer 116 to be separated, andthe plastic substrate 110. The end portion of the metal substrate 401 isoutside the peripheral portions of the second adhesive layer 400, thelight-emitting element 518, the layer 116 to be separated, and theplastic substrate 110. In addition, a sealing film 521 covers the secondadhesive layer 400, the light-emitting element 518, the layer 116 to beseparated, and the plastic substrate 110, and is in contact with thesurface of the metal substrate 401. The sealing film 521 is formed usinga material having low permeability and a light-transmitting propertywith respect to visible light. Typically, an inorganic material such asan insulating film containing nitrogen and silicon, e.g., a siliconnitride film, a silicon nitride oxide film, or a silicon oxynitride filmis preferably used. The sealing film 521 with such a structure canprevent moisture from entering the light-emitting device from the endportions and the interfaces of the second adhesive layer 400, thelight-emitting element 518, the layer 116 to be separated, and theplastic substrate 110 which are included in the light-emitting device.

In addition, the light-emitting device illustrated in FIG. 11B isprovided with a planarization layer 522 at the end portions of thesecond adhesive layer 400, the light-emitting element 518, the layer 116to be separated, and the plastic substrate 110. The planarization layer522 can be formed using a resin. With the planarization layer 522, astep formed by the stacked layer structure of the second adhesive layer400, the light-emitting element 518, the layer 116 to be separated, andthe plastic substrate 110 can be reduced. The sealing film 521 caneasily cover the end portions where the step has become gentle with theplanarization layer 522. With this structure, the sealing film 521 canmore effectively prevent moisture from entering the light-emittingdevice from the end portions and the interfaces of the second adhesivelayer 400, the light-emitting element 518, the layer 116 to beseparated, and the plastic substrate 110 which are included in thelight-emitting device. Note that the planarization layer 522 may beformed by coating so as to cover not only the end portions but also theentire surface of the plastic substrate 110.

As described above, in the flexible light-emitting device described inthis embodiment, a TFT can be formed over a formation substrate withhigh heat resistance and thus a TFT using a crystalline semiconductorlayer such as crystalline silicon having high mobility can be formed.Accordingly, a driver circuit portion can be partially formed at thesame time when a pixel portion is formed, whereby the flexiblelight-emitting device can be manufactured at lower cost.

Embodiment 2

In this embodiment, an electronic device including the light-emittingdevice described in Embodiment 1 as a part thereof will be described.

Examples of the electronic device including the light-emitting elementdescribed in Embodiment 1 include cameras such as video cameras ordigital cameras, goggle type displays, navigation systems, audioplayback devices (e.g., car audio systems and audio systems), computers,game machines, portable information terminals (e.g., mobile computers,mobile phones, portable game machines, and electronic book devices),image playback devices in which a recording medium is provided(specifically, devices that are capable of playing back recording mediasuch as digital versatile discs (DVDs) and equipped with a display unitthat can display images), and the like. Such electronic devices areillustrated in FIGS. 5A to 5E.

FIG. 5A illustrates a television device which includes a housing 9101, asupport 9102, a display portion 9103, speaker portions 9104, video inputterminals 9105, and the like. In this television device, the displayportion 9103 is manufactured using the light-emitting device describedin Embodiment 1. The television device is provided with thelight-emitting device described in Embodiment 1 which is flexible, haslong lifetime, and can easily be manufactured. The display portion 9103can perform display also when being curved and is lightweight, and thus,the television device can be a relatively inexpensive product with longlifetime.

FIG. 5B illustrates a computer which includes a main body 9201, ahousing 9202, a display portion 9203, a keyboard 9204, an externalconnection port 9205, a pointing device 9206, and the like. In thiscomputer, the display portion 9203 is manufactured using thelight-emitting device described in Embodiment 1. The computer isprovided with the light-emitting device described in Embodiment 1 whichis flexible, has long lifetime, and can easily be manufactured. Thedisplay portion 9203 can perform display also when being curved and islightweight, and thus, the computer can be a relatively inexpensiveproduct with long lifetime.

FIG. 5C illustrates a mobile phone which includes a main body 9401, ahousing 9402, a display portion 9403, an audio input portion 9404, anaudio output portion 9405, operation keys 9406, an external connectionport 9407, and the like. In this mobile phone, the display portion 9403is manufactured using the light-emitting device described inEmbodiment 1. The mobile phone is provided with the light-emittingdevice described in Embodiment 1 which is flexible, has long lifetime,and can easily be manufactured. The display portion 9403 can performdisplay also when being curved and is lightweight and furthermore canprovide images with high quality. The lightweight mobile phone of thisembodiment can have appropriate weight for being carried even when avariety of additional values are added thereto, and thus the mobilephone is also suitable for use as a highly functional mobile phone.

FIG. 5D illustrates a camera which includes a main body 9501, a displayportion 9502, a housing 9503, an external connection port 9504, a remotecontrol receiving portion 9505, an image receiving portion 9506, abattery 9507, an audio input portion 9508, operation keys 9509, aneyepiece portion 9510, and the like. In this camera, the display portion9502 is manufactured using the light-emitting device described inEmbodiment 1. The camera is provided with the light-emitting devicedescribed in Embodiment 1 which is flexible, has long lifetime, and caneasily be manufactured. The display portion 9502 can perform displayalso when being curved and is lightweight, and thus, the camera can be arelatively inexpensive product with long lifetime.

FIG. 5E illustrates a display which includes a main body 9601, a displayportion 9602, an external memory insertion portion 9603, a speakerportion 9604, operation keys 9605, and the like. The main body 9601 maybe provided with an antenna for receiving a television broadcast, anexternal input terminal, an external output terminal, a battery, and thelike. In this display, the display portion 9602 is manufactured usingthe light-emitting device described in Embodiment 1. The flexibledisplay portion 9602 can be rolled up and stored in the main body 9601and is suitable for being carried. The display is provided with thelight-emitting device described in Embodiment 1 which is flexible, haslong lifetime, and can easily be manufactured. The display portion 9602can be suitable for being carried and is lightweight, and thus, thedisplay can be a relatively inexpensive product with long lifetime.

As described above, the application range of the light-emitting devicedescribed in Embodiment 1 is so wide that the light-emitting device canbe applied to electronic devices of various fields.

Embodiment 3

Since a plastic substrate is used for a flexible light-emitting device,a flexible light-emitting device is more often electrically charged thana light-emitting device using a glass substrate or the like. Therefore,in this embodiment, an example is shown, in which a transparentconductive film is used for the coat film 124 in FIG. 1C to manufacturea flexible light-emitting device which is resistant to staticelectricity.

A structure in which the coat film 124 which is a transparent conductivefilm is provided on the surface of the plastic substrate 110, which isopposite to the surface in contact with the first adhesive layer 111, isemployed. The coat film 124 which is a transparent conductive film maybe formed after the FPC 402 is attached, after the metal substrate 401is attached, or before the FPC 402 is attached.

A transparent conductive film which is used for the coat film 124 isformed using indium oxide (In₂O₃), tin oxide, an alloy of indium oxideand tin oxide (In₂O₃—SnO₂, abbreviated to ITO), indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium zinc oxide, indium tin oxide towhich silicon oxide is added, antimony oxide, or the like by asputtering method, a printing method, a vacuum evaporation method, orthe like.

With the above structure, even when an electrostatically-charged hand,finger, or the like of the human touches the plastic substrate 110covered with the coat film 124 which is a transparent conductive filmand electricity is discharged, the TFTs (such as the n-channel TFT 513and the p-channel TFT 514) and the pixel portion 502 can be protected.

In addition, the coat film 124 which is a transparent conductive filmcan protect the surface of the soft plastic substrate 110 from scratchesand the like.

Further, the coat film 124 which is a transparent conductive film andthe metal substrate 401 preferably have electrical continuitytherebetween, and FIGS. 12A to 12C illustrate examples of such astructure. In this case, a conductive substrate is used for the metalsubstrate 401.

FIGS. 12A to 12C are only partially different from FIGS. 4A to 4C, andthus, identical portions are denoted by the same reference numerals.

FIG. 12A is a top view illustrating an EL module, and FIG. 12B is across-sectional view along chain line A-A′ of FIG. 12A. FIG. 12C is across-sectional view along dotted line X-Y of FIG. 12A.

In FIG. 12A, a protective film 501 is provided over a plastic substrate110 with a first adhesive layer 500 interposed therebetween. Over theprotective film 501, a pixel portion 502, a source side driver circuit504, and a gate side driver circuit 503 are formed. These pixel portionand driver circuits can be obtained as described in Embodiment 1.

Reference numeral 400 denotes a second adhesive layer and referencenumeral 401 denotes a metal substrate. The second adhesive layer 400 isformed over the pixel portion and the driver circuit portions, and themetal substrate 401 is adhered with the second adhesive layer 400. Themetal substrate 401 has a region which does not overlap with the plasticsubstrate 110, and a coat film 124 which is a transparent conductivefilm is formed on that region. In addition, the coat film 124 which is atransparent conductive film is also formed on the side surface of theplastic substrate 110, the side surface of the first adhesive layer 500,the side surface of the protective film 501, the side surface of a gateinsulating film, the side surface of an interlayer insulating film, theside surface of the second adhesive layer 400, and the like. The coatfilm 124 which is a transparent conductive film is formed on these sidesurfaces, whereby the metal substrate 401 and the coat film 124 haveelectrical continuity therebetween.

In addition, the metal substrate 401 and the coat film 124 are disposedso as to surround the plastic substrate 110 as illustrated in FIG. 12Cand thus the metal substrate and the coat film 124 have electricalcontinuity therebetween, whereby the flexible light-emitting device canbe effectively prevented from being electrostatically-charged.

In this embodiment, a film of an alloy of indium oxide and tin oxidewith a thickness of 110 nm is formed on the plastic substrate 110 andthe metal substrate 401 which is a stainless steel substrate.

While the transparent conductive film is formed by a sputtering method,the FPC 402 is protected by being covered with a metal foil or the likeso that the transparent conductive film is not formed at an end portionof the FPC 402. It is preferable to form the transparent conductive filmalso on the side surfaces described above and a part of the metalsubstrate 401 (a region which does not overlap with the plasticsubstrate 110). Although not illustrated, if the FPC 402 is notprotected by being covered with a metal foil or the like, thetransparent conductive film is also formed on the FPC 402.

In addition, the coat film 124 which is a transparent conductive filmcan protect the surface of the soft plastic substrate 110 from scratchesand the like. Furthermore, the coat film 124 which is a transparentconductive film provided on the side surfaces also serves as aprotective film which suppresses moisture entering the light-emittingdevice.

This embodiment can be freely combined with any of other embodiments.

Example 1

In this example, an active matrix flexible light-emitting device whichcan be used for an image display device will be described. FIGS. 7A and7B each illustrate a structure of the light-emitting device described inthis example. FIG. 7A is a top view of the active matrix light-emittingdevice, and FIG. 7B is a cross-sectional view along line A-A′ of FIG.7A.

The flexible light-emitting device which is described in this exampleincludes a plastic substrate 110, a layer 116 to be separated, alight-emitting element 518, and a metal substrate 401.

The plastic substrate 110 to which the layer 116 to be separated istransferred is formed using an aramid film whose light-transmittingproperty with respect to visible light is greater than or equal to 90%,thermal expansion coefficient is about 10 ppm/K, and thickness is 20 μm.In addition, a first adhesive layer 500 with which the plastic substrate110 and the layer 116 to be separated are adhered to each other isformed using a two component type epoxy adhesive (R2007/H-1010, producedby ALTECO INC.).

The layer 116 to be separated includes a protective film 501, a pixelportion 502, a gate side driver circuit 503, and a source side drivercircuit 504. In addition, the pixel portion 502 includes a currentcontrol TFT 511 and a pixel electrode 512. The pixel electrode 512 iselectrically connected to a drain electrode layer of the current controlTFT 511. The current control TFT 511 is a p-channel TFT and the pixelelectrode 512 is an anode of the light-emitting element 518.

The protective film 501 is formed using a multi-layer film including asilicon oxynitride (SiOxNy, x>y) layer with a thickness of 200 nm, asilicon nitride (SiNy) layer with a thickness of 200 nm, a siliconoxynitride (SiOxNy, x>y) layer with a thickness of 200 nm, a siliconnitride oxide (SiNyOx, x<y) layer with a thickness of 140 nm, and asilicon oxynitride (SiOxNy, x>y) layer with a thickness of 100 nm. Withsuch a multi-layer structure, water vapor or oxygen can be preventedfrom entering the light-emitting device from the lower portion of thesubstrate.

The TFT described in this example is a staggered TFT in which a gateinsulating film is provided over a semiconductor layer, a gate electrodelayer is provided so as to overlap with the semiconductor layer with thegate insulating film interposed therebetween, and a source electrodelayer and a drain electrode layer which are electrically connect asource region and a drain region respectively of the semiconductor layerare provided. The semiconductor layer of the TFT is formed using apolysilicon layer with a thickness of 50 nm, and the gate insulatingfilm thereof is formed using a silicon oxynitride (SiOxNy, x>y) filmwith a thickness of 110 nm.

Although not illustrated, the gate electrode layer includes two layers,and a lower layer of the gate electrode layer is longer than an upperlayer thereof. The lower layer of the gate electrode layer is formedusing a tantalum nitride layer with a thickness of 30 nm, and the upperlayer thereof is formed using a tungsten (W) layer with a thickness of370 nm. With such a structure, a lightly doped drain (LDD) region can beformed without using another photomask.

A first interlayer insulating film 515 a which is formed over the gateinsulating film and the gate electrode layer is formed using amulti-layer film in which a silicon oxynitride (SiOxNy, x>y) layer witha thickness of 50 nm, a silicon nitride oxide (SiNyOx, x<y) layer with athickness of 140 nm, and a silicon oxynitride (SiOxNy, x>y) layer with athickness of 520 nm are stacked.

The source electrode layer and the drain electrode layer are formed soas to be connected to the source region and the drain regionrespectively of the TFT through contact holes in the first interlayerinsulating film 515 a. The source and drain electrode layers are formedusing a multi-layer film including a titanium layer with a thickness of100 nm, an aluminum layer with a thickness of 700 nm, and a titaniumlayer with a thickness of 100 nm. In this manner, by stacking aluminumwith low electric resistance and titanium with excellent heatresistance, it is possible to suppress wiring resistance and preventgeneration of a hillock in the process. A wiring layer is also formedusing the same multi-layer although not illustrated.

A second interlayer insulating film 515 b which is formed over the TFTis formed using a silicon oxynitride (SiOxNy, x>y) layer with athickness of 150 nm.

The pixel electrode (first electrode) 512 is formed using a film ofindium tin oxide containing silicon oxide (ITSO) with a thickness of 125nm. In addition, an end portion of the pixel electrode 512 is coveredwith a partition wall 519 which is formed using photosensitivepolyimide. The end portion of the partition wall 519 is in contact withthe surface of the pixel electrode 512 and has a gentle angle. A step atthe end portion of the partition wall 519 which has a gentle angle andis in contact with the surface of the pixel electrode 512 is reduced,and in a light-emitting element in which the pixel electrode 512 servesas one electrode, the pixel electrode 512 and the other electrode arenot easily short-circuited.

In this example, the layer 116 to be separated is formed over aseparation layer which is formed over a glass substrate (AN100, producedby Asahi Glass Co., Ltd.) with a thickness of 0.7 mm. The separationlayer is formed using a multi-layer film in which a silicon oxynitride(SiOxNy, x>y) layer with a thickness of 100 nm and a tungsten layer witha thickness of 50 nm are stacked.

FIG. 7C illustrates the structure of the light-emitting element 518 inwhich the pixel electrode 512 serves as one electrode. In thelight-emitting element 518, the pixel electrode 512 serves as a firstelectrode, and an EL layer 516 is provided between a second electrode517 and the pixel electrode 512. Chemical formulas of materials used inthis example are shown below.

A manufacturing method of the light-emitting element of this example isdescribed below.

First, a substrate provided with the pixel electrode 512 was fixed to asubstrate holder in a vacuum evaporation apparatus so that the surfaceof the substrate, on which the pixel electrode 512 was formed, faceddownward. After the pressure was lowered to approximately 10⁻⁴ Pa, afirst layer 2111 containing a composite material of an organic compoundand an inorganic compound was formed on the pixel electrode 512 as ahole-injecting layer by co-evaporation of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) and molybdenum(VI)oxide. The thickness of the first layer 2111 was 140 nm, and the weightratio of NPB to molybdenum(VI) oxide was adjusted to be 1:0.11(=NPB:molybdenum oxide). A co-evaporation method is an evaporationmethod by which evaporation is performed from a plurality of evaporationsources at the same time in one treatment chamber.

Next, an NPB film was formed so as to have a thickness of 10 nm on thefirst layer 2111 containing a composite material by an evaporationmethod using resistive heating to form a second layer 2112 as ahole-transporting layer.

Then, a third layer 2113 was formed as a light-emitting layer on thesecond layer 2112 by co-evaporation of9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (CzPA) andN-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (2PCAPA)which is a green light-emitting substance. The thickness of thelight-emitting layer was set to be 30 nm, and the evaporation rate wasadjusted such that the weight ratio of CzPA to 2PCAPA was 1:0.05 (=CzPA:2PCAPA).

Then, tris(8-quinolinolato)aluminum (Alq) and N,N-diphenylquinacridone(DPQd) which is an electron-trapping substance were co-evaporated on thethird layer 2113, so that a first electron-transporting region 2114 awas formed. The thickness of the first electron-transporting region 2114a was set to be 10 nm, and the evaporation rate was adjusted such thatthe weight ratio of Alq to DPQd was 1:0.005 (=Alq:DPQd).

After that, as a second electron-transporting region 2114 b,bathophenanthroline (BPhen) was evaporated to a thickness of 30 nm.Accordingly, a fourth layer 2114 including the firstelectron-transporting region 2114 a and the second electron-transportingregion 2114 b was formed as an electron-transporting layer.

Further, lithium fluoride (LiF) was evaporated on the fourth layer 2114,whereby a fifth layer 2115 was formed as an electron-injecting layer.The thickness of the fifth layer 2115 was set to be 1 nm.

Finally, the second electrode 517 serving as a cathode was formed. Thesecond electrode 517 was formed to include two layers. A firstconductive layer 517 a which was in contact with the fifth layer 2115was formed by co-evaporation of aluminum (Al) and NPB. The weight ratioof aluminum to NPB was adjusted to be 5:1 (=Al:NPB). In addition, thethickness of the first conductive layer 517 a was set to be 100 nm.Further, as a second conductive layer 517 b, aluminum was evaporated onthe first conductive layer 517 a to have a thickness of 100 nm. Notethat the second electrode 517 was connected to a terminal portionthrough a common electrode layer.

Further, in the above evaporation processes, a resistive heating methodcan be used for each evaporation.

The metal substrate 401 is attached to the layer 116 to be separated andthe light-emitting element 518 (the pixel electrode 512 is included inthe light-emitting element 518) with an second adhesive layer 400interposed therebetween, thereby preventing the layer 116 to beseparated and the light-emitting element 518 from being exposed to theair. The metal substrate 401 is formed with a ferritic stainless steelsubstrate (YUS205-M1, produced by Nippon Steel Materials Co., Ltd.)whose thermal expansion coefficient is about 10 ppm/K and thickness is20 μm. The second adhesive layer 400 is formed with an acrylic sheetadhesive (8171J, produced by Sumitomo 3M Limited) which is 25 μm thick.

The light-emitting device described in this example is manufactured bythe manufacturing method described in Embodiment 1. That is, first, thelayer 116 to be separated including the protective film 501, the pixelelectrode 512 serving as a first electrode, and the like was formed overthe separation layer which was formed over the formation substrate.Then, the layer 116 to be separated was transferred from the formationsubstrate to the plastic substrate 110 which had a light-transmittingproperty with respect to visible light and flexibility, using atemporary supporting substrate. After that, the EL layer 516 and thesecond electrode 517 were formed over the pixel electrode 512 to formthe light-emitting element 518. Finally, the layer 116 to be separatedand the light-emitting element 518 were sealed by the metal substrate401 using the second adhesive layer 400, whereby the light-emittingdevice was manufactured.

The flexible light-emitting device described in this example was drivenwhile being wrapped around a cylinder whose diameter was 10 mm and avideo signal was input. The light-emitting device responded to the videosignal and operated normally while being bent into a cylindrical shape.Further, when the light-emitting device was taken off the cylinder anddriven, it operated normally in a flat shape. Photographs oflight-emitting states are shown in FIG. 9.

The light-emitting device described in this example includes the layerto be separated which is formed using the formation substrate havinghigh heat resistance. As a result, the layer to be separated can beformed using a high-temperature process; thus, the protective film witha high moisture-proof property can be easily formed, and thelight-emitting element can be surely and inexpensively protected. Inaddition, the light-emitting device in this example is flexible and canemit light either in a bent state or a flat state.

The light-emitting device in this example is constructed by a thin filmand a metal thin plate. Therefore, the light-emitting device islightweight and less deformed even when being dropped; moreover, sinceit is highly flat and less curls along with the change in useenvironment, the driver circuit of the display device is broken withdifficulty. Accordingly, the light-emitting device in this example issuitable to the use in flexible displays.

Example 2

In this example, a flexible light-emitting device which can be used asboth a display device and a lighting device will be described. In thelight-emitting device of this example, electrode layers of a pluralityof light-emitting elements which are connected to a terminal portionwithout a switching element interposed therebetween are arranged inmatrix. Thus, the light-emitting device can be called a passive matrixtype and can be used for display devices or backlights of displaydevices. Note that the light-emitting device can be used as a lightingdevice even when not a plurality of light-emitting elements but a singlelight-emitting element is arranged therein.

FIGS. 8A and 8B illustrate a structure of a pixel portion of thelight-emitting device in this example. FIG. 8A is a top viewillustrating the passive matrix light-emitting device and FIG. 8B is across-sectional view taken along line A-A′ of FIG. 8A.

The flexible light-emitting device of this example includes a plasticsubstrate 110, a layer 116 to be separated, a light-emitting element518, and a metal substrate 401. The plastic substrate 110, thelight-emitting element 518, and the metal substrate 401 are the same asin Example 1 and thus the description thereof is omitted.

The layer 116 to be separated of this example includes a protective film501, a pixel electrode 512, interlayer insulating films 515 a and 515 b,and a partition wall 519.

The protective film 501 is formed with a multi-layer film including asilicon oxynitride (SiOxNy, x>y) layer with a thickness of 200 nm, asilicon nitride (SiNy) layer with a thickness of 200 nm, a siliconoxynitride (SiOxNy, x>y) layer with a thickness of 200 nm, a siliconnitride oxide (SiNyOx, x<y) layer with a thickness of 140 nm, and asilicon oxynitride (SiOxNy, x>y) layer with a thickness of 100 nm (seeFIG. 13).

The first interlayer insulating film 515 a is formed using a multi-layerfilm including a silicon oxynitride (SiOxNy, x>y) layer with a thicknessof 50 nm, a silicon nitride oxide (SiNyOx, x<y) layer with a thicknessof 140 nm, and a silicon oxynitride (SiOxNy, x>y) layer with a thicknessof 520 nm.

A wiring layer is formed using a multi-layer film including a titaniumlayer with a thickness of 100 nm, an aluminum layer with a thickness of700 nm, and a titanium layer with a thickness of 100 nm. In addition,the second interlayer insulating film 515 b is formed using a siliconoxynitride (SiOxNy, x>y) layer with a thickness of 150 nm.

The pixel electrode 512 is electrically connected to the wiring layerthrough a contact hole in the second interlayer insulating film 515 b.The pixel electrode 512 is formed using a film of indium tin oxidecontaining silicon oxide (ITSO) with a thickness of 125 nm.

In addition, an end portion of the pixel electrode 512 is covered withthe partition wall 519 which is formed using photosensitive polyimide.

In this example, the layer 116 to be separated was formed over theseparation layer which was formed over a glass substrate with athickness of 0.7 mm. The separation layer is formed using a multi-layerfilm in which a silicon oxynitride (SiOxNy, x>y) layer with a thicknessof 100 nm and a tungsten layer with a thickness of 50 nm are stacked.

The flexible light-emitting device in this example was driven whilebeing wrapped around a cylinder whose diameter is 5 mm to 30 mm. Thelight-emitting device emitted light and operated normally while beingbent into a cylindrical shape. Further, when the light-emitting devicewas taken off the cylinder and driven, it emitted light normally in aflat shape, and also emitted light normally even when the light-emittingdevice was repeatedly wrapped around and taken off the cylinder.Photographs showing light-emitting states are shown in FIG. 10.

The light-emitting device in this example includes the layer to beseparated which is formed using the formation substrate having high heatresistance. As a result, the layer to be separated can be formed using ahigh-temperature process; thus, the protective film with a highmoisture-proof property can be easily formed, and the light-emittingelement can be surely and inexpensively protected. In addition, thelight-emitting device in this example is flexible and can emit lighteither in a bent state or a flat state.

The light-emitting device in this example is constructed by a thin filmand a metal thin plate. Since the light-emitting device is thin, it canbe placed in a narrow space or disposed by being deformed along a curvedsurface. In addition, the light-emitting device is lightweight and thusis suitable to the use in a device whose weight is strictly restricted,such as a portable device or an airplane.

This application is based on Japanese Patent Application serial no.2008-267774 filed with Japan Patent Office on Oct. 16, 2008, andJapanese Patent Application serial no. 2009-123451 filed with JapanPatent Office on May 21, 2009, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. A light-emitting device comprising: a substratehaving light-transmitting property with respect to visible light; afirst insulating layer over the substrate; a second insulating layerover the first insulating layer; a third insulating layer over thesecond insulating layer; a light-emitting element over the thirdinsulating layer; and a metal substrate over the light-emitting element,wherein the light-emitting element comprises a first light-emittinglayer and a second light-emitting layer over the first light-emittinglayer, wherein the first light-emitting layer comprises a fluorescentmaterial, wherein the second light-emitting layer comprises aphosphorescent material, wherein oxygen content in the first insulatinglayer is larger than nitrogen content in the first insulating layer,wherein nitrogen content in the second insulating layer is larger thanoxygen content in the second insulating layer, and wherein oxygencontent in the third insulating layer is larger than nitrogen content inthe third insulating layer.
 2. The light-emitting device according toclaim 1, wherein the fluorescent material is a blue fluorescentmaterial.
 3. The light-emitting device according to claim 1, wherein thephosphorescent material is a red phosphorescent material.
 4. Thelight-emitting device according to claim 1, further comprising a chargegeneration layer between the first light-emitting layer and the secondlight-emitting layer.
 5. The light-emitting device according to claim 1,wherein the light-emitting element emits white light.
 6. Thelight-emitting device according to claim 1, further comprising a colorfilter overlapping with the light-emitting element.
 7. Thelight-emitting device according to claim 1, wherein the light-emittingdevice is a bottom emission light-emitting device.
 8. A light-emittingdevice comprising: a substrate having light-transmitting property withrespect to visible light; a first insulating layer over the substrate; asecond insulating layer over the first insulating layer; a thirdinsulating layer over the second insulating layer; a transistor over thethird insulating layer; a light-emitting element over the thirdinsulating layer and the transistor; a color filter between thetransistor and the light-emitting element; and a metal substrate overthe light-emitting element, wherein the light-emitting element comprisesa first light-emitting layer and a second light-emitting layer over thefirst light-emitting layer, wherein the first light-emitting layercomprises a fluorescent material, and wherein the second light-emittinglayer comprises a phosphorescent material, wherein oxygen content in thefirst insulating layer is larger than nitrogen content in the firstinsulating layer, wherein nitrogen content in the second insulatinglayer is larger than oxygen content in the second insulating layer, andwherein oxygen content in the third insulating layer is larger thannitrogen content in the third insulating layer.
 9. The light-emittingdevice according to claim 8, wherein the fluorescent material is a bluefluorescent material.
 10. The light-emitting device according to claim8, wherein the phosphorescent material is a red phosphorescent material.11. The light-emitting device according to claim 8, further comprising acharge generation layer between the first light-emitting layer and thesecond light-emitting layer.
 12. The light-emitting device according toclaim 8, wherein the light-emitting element emits white light.
 13. Thelight-emitting device according to claim 8, wherein the light-emittingdevice is a bottom emission light-emitting device.
 14. A light-emittingdevice comprising: a substrate having light-transmitting property withrespect to visible light; a first insulating layer over the substrate; asecond insulating layer over the first insulating layer; a thirdinsulating layer over the second insulating layer; a light-emittingelement over the third insulating layer; and a metal substrate over thelight-emitting element, wherein the light-emitting element comprises afirst light-emitting layer and a second light-emitting layer over thefirst light-emitting layer, wherein light emission from the firstlight-emitting layer and light emission from the second light-emittinglayer have complementary colors to each other, wherein the lightemission from the first light-emitting layer is blue, wherein oxygencontent in the first insulating layer is larger than nitrogen content inthe first insulating layer, wherein nitrogen content in the secondinsulating layer is larger than oxygen content in the second insulatinglayer, and wherein oxygen content in the third insulating layer islarger than nitrogen content in the third insulating layer.
 15. Thelight-emitting device according to claim 14, wherein the light emissionfrom the second light-emitting layer is yellow.
 16. The light-emittingdevice according to claim 14, wherein the first light-emitting layercomprises a fluorescent material, and wherein the second light-emittinglayer comprises a phosphorescent material.
 17. The light-emitting deviceaccording to claim 14, wherein the light-emitting element emits whitelight.
 18. The light-emitting device according to claim 14, furthercomprising a color filter overlapping with the light-emitting element.19. The light-emitting device according to claim 14, wherein thelight-emitting device is a bottom emission light-emitting device.